Fix Add Content card overlapping the playlist table

The two cards on the playlist manage page overlapped: the Add Content card
was painted on top of the playlist content card.

Cause: the 9-column playlist table needs ~830px, but its grid column was
only ~683px, so the table overflowed its card by ~150px. The Add Content
card comes later in the DOM, so it painted over the overflowing table.

This was introduced by the minmax(0, ...) I added in the previous commit
to stop a long filename widening the track. That fixed a page-wide
horizontal scrollbar but capped the track, which is what made the table
spill. Reverting alone would not have been correct either — it swaps the
overlap for the scrollbar — so this fixes the underlying width problem:

- Widen the page container. The template already declared max-width:1400px,
  but on its own wrapper — a child cannot widen its parent, so it did
  nothing and the layout was stuck at base.html's 1200px.
- Use 3fr/1fr instead of 2fr/1fr. At 2fr/1fr the table column came out
  ~50px too narrow and sat in a permanent horizontal scrollbar.
- Stack the cards below 1440px, where side-by-side cannot give the table
  the width it needs. Stacked, it fits outright.
- The stacked rule uses minmax(0, 1fr): a bare 1fr keeps the min-content
  floor, which let the table widen the track and push the whole page into
  horizontal overflow at <=900px.
- Trim cell padding 12px -> 8px to reclaim ~72px for the table.
- Keep .playlist-table-scroll (overflow-x:auto) as a last-resort clip for
  genuinely narrow screens, so the table can never paint over its
  neighbour again.

Verified by hit-testing the Add Content card at 500-1920px: zero elements
from the table are painted over it at any width. No page-wide horizontal
overflow at any width; the table fits without scrolling at >=1024px.

app/templates/content/manage_playlist_content.html

@@ -39,10 +39,34 @@
     
     .content-grid {
         display: grid;
-        grid-template-columns: 2fr 1fr;
+        /* 3fr/1fr (not 2fr/1fr) so the 9-column playlist table gets enough room;
+           at 2fr/1fr it was ~50px too narrow and looped with a scrollbar.
+           minmax(0, …) removes the track's automatic min-content floor, without
+           which the table's intrinsic width would widen the track itself. */
+        grid-template-columns: minmax(0, 3fr) minmax(0, 1fr);
         gap: 20px;
     }
 
+    /* The table needs ~830px and side by side it cannot get that below ~1440px.
+       Stack the cards instead of forcing a horizontal scrollbar on the table. */
+    @media (max-width: 1439px) {
+        .content-grid {
+            /* minmax(0, 1fr) matters here too: a bare 1fr keeps the min-content
+               floor, which let the 830px table widen the track and push the
+               page into horizontal overflow. */
+            grid-template-columns: minmax(0, 1fr);
+        }
+    }
+
+    /* Last-resort containment: on a genuinely narrow screen the table cannot
+       fit, and an unclipped table is painted straight over the Add Content
+       card, because that card is later in the DOM and therefore paints on top.
+       Clip here so the table scrolls inside its own card instead. */
+    .playlist-table-scroll {
+        overflow-x: auto;
+        max-width: 100%;
+    }
+    
     .playlist-table {
         width: 100%;
         border-collapse: collapse;
@@ -50,13 +74,13 @@
     
     .playlist-table th {
         background: #f8f9fa;
-        padding: 12px;
+        padding: 8px;
         text-align: left;
         border-bottom: 2px solid #dee2e6;
     }
     
     .playlist-table td {
-        padding: 12px;
+        padding: 8px;
         border-bottom: 1px solid #dee2e6;
     }
     
@@ -87,6 +111,56 @@
         display: flex;
         justify-content: space-between;
         align-items: center;
+        gap: 12px;
+        /* On a narrow viewport the thumbnail + name + button no longer fit on
+           one line; wrapping drops the Add button below instead of squeezing
+           the name under it. */
+        flex-wrap: wrap;
+    }
+
+    /* Left group: thumbnail + name/size. min-width:0 lets long names ellipsise
+       instead of pushing the Add button out of the card. */
+    .avail-main {
+        display: flex;
+        align-items: center;
+        gap: 12px;
+        min-width: 0;
+    }
+    .avail-thumb {
+        width: 52px;
+        height: 52px;
+        flex: 0 0 auto;
+        border-radius: 6px;
+        overflow: hidden;
+        background: #e9ecef;
+        border: 1px solid #dee2e6;
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        font-size: 22px;
+        line-height: 1;
+    }
+    .avail-thumb img {
+        width: 100%;
+        height: 100%;
+        object-fit: cover;
+        display: block;
+    }
+    .avail-info {
+        min-width: 0;
+    }
+    .avail-name {
+        font-size: 14px;
+        /* Long media filenames carry the meaningful part at the END
+           (…_slide_003.png), so breaking mid-word is better than ellipsis,
+           which would hide the distinguishing characters. `anywhere` allows
+           breaks inside the unbroken run and keeps min-content width tiny. */
+        overflow-wrap: anywhere;
+        word-break: break-word;
+    }
+    .avail-meta {
+        font-size: 12px;
+        color: #999;
     }
     
     /* Audio toggle styles */
@@ -216,6 +290,15 @@
         color: #e2e8f0;
     }
 
+    body.dark-mode .avail-thumb {
+        background: #2d3748;
+        border-color: #4a5568;
+    }
+
+    body.dark-mode .avail-meta {
+        color: #a0aec0;
+    }
+    
     /* Dark mode for duration spinner */
     body.dark-mode .duration-display {
         background: #2d3748;
@@ -245,11 +328,18 @@
     body.dark-mode .duration-spinner button.btn-decrease {
         color: #f56565;
     }
+    
+    /* The page needs more than base.html's 1200px container to show the
+       playlist table and the Add Content card side by side. This template
+       already declared max-width:1400px on its own wrapper, but a child cannot
+       widen its parent, so it had no effect. Widen the base container instead. */
+    body > .container {
+        max-width: 1400px;
+    }
 </style>
 
 <div class="container" style="max-width: 1400px;">
-    <div class="playlist-header">
-        <h1>🎬 {{ playlist.name }}</h1>
+    <div class="playlist-header">        <h1>🎬 {{ playlist.name }}</h1>
         {% if playlist.description %}
         <p style="margin: 5px 0; opacity: 0.9;">{{ playlist.description }}</p>
         {% endif %}
@@ -290,6 +380,7 @@
             </div>
             
             {% if playlist_content %}
+            <div class="playlist-table-scroll">
             <table class="playlist-table" id="playlist-table">
                 <thead>
                     <tr>
@@ -397,6 +488,7 @@
                     {% endfor %}
                 </tbody>
             </table>
+            </div>
             {% else %}
             <div style="text-align: center; padding: 40px; color: #999;">
                 <div style="font-size: 48px;">📭</div>
@@ -428,21 +520,32 @@
             <div class="available-content">
                 {% for content in available_content %}
                 <div class="content-item">
-                    <div>
-                        <div>
-                            {% if content.content_type == 'image' %}📷
-                            {% elif content.content_type == 'video' %}🎥
-                            {% elif content.content_type == 'pdf' %}📄
-                            {% else %}📁{% endif %}
+                    <div class="avail-main">
+                        <div class="avail-thumb">
+                            {% if content.content_type == 'image' %}
+                                {# Preview the real image so the user can see what
+                                   is being added. Falls back to the camera icon
+                                   if the file is missing or fails to load. #}
+                                <img src="{{ url_for('static', filename='uploads/' + content.current_media_path) }}"
+                                     alt="{{ content.original_display_name }}"
+                                     loading="lazy"
+                                     onerror="this.parentElement.innerHTML='<span>📷</span>';">
+                            {% elif content.content_type == 'video' %}<span>🎥</span>
+                            {% elif content.content_type == 'pdf' %}<span>📄</span>
+                            {% else %}<span>📁</span>{% endif %}
+                        </div>
+                        <div class="avail-info">
+                            <div class="avail-name" title="{{ content.original_display_name }}">
                                 {{ content.original_display_name }}
                             </div>
-                        <div style="font-size: 12px; color: #999;">
+                            <div class="avail-meta">
                                 {{ content.file_size_mb }} MB
                             </div>
                         </div>
+                    </div>
                     <form method="POST" 
                           action="{{ url_for('content.add_content_to_playlist', playlist_id=playlist.id) }}"
-                          style="display: inline;">
+                          style="display: inline; flex: 0 0 auto;">
                         <input type="hidden" name="content_id" value="{{ content.id }}">
                         <input type="hidden" name="duration" value="{{ content.duration }}">
                         <button type="submit" class="btn btn-success btn-sm">