Add dark mode support and replace group assignment with playlist assignment

- Added comprehensive dark mode styling to all pages:
  * Dashboard (workflow guide, secondary text, log items)
  * Admin panel with user management system
  * Content/playlist management page
  * Upload media page
  * Add player page

- Implemented user management system:
  * Create/edit/delete users
  * Two role types (user/admin)
  * Reset password functionality
  * Role-based permissions

- Replaced group assignment with playlist assignment:
  * Players now directly assigned to playlists
  * Updated add player form and backend
  * Removed group selection from player creation

- Fixed bugs:
  * Updated instance_path configuration for SQLite
  * Fixed import path in app factory
  * Updated dependencies (Pillow 11.0.0, removed gevent)

- Added start.sh script for easy development server launch

app/templates/dashboard.html

@@ -30,7 +30,7 @@
             Media Library
         </h3>
         <p style="font-size: 2rem; font-weight: bold;">{{ total_content or 0 }}</p>
-        <p style="font-size: 0.9rem; color: #7f8c8d; margin-top: 0.5rem;">Unique media files</p>
+        <p class="secondary-text" style="font-size: 0.9rem; margin-top: 0.5rem;">Unique media files</p>
     </div>
     
     <div class="card">
@@ -39,7 +39,7 @@
             Storage
         </h3>
         <p style="font-size: 2rem; font-weight: bold;">{{ storage_mb or 0 }} MB</p>
-        <p style="font-size: 0.9rem; color: #7f8c8d; margin-top: 0.5rem;">Total uploads</p>
+        <p class="secondary-text" style="font-size: 0.9rem; margin-top: 0.5rem;">Total uploads</p>
     </div>
 </div>
 
@@ -69,7 +69,7 @@
         <img src="{{ url_for('static', filename='icons/info.svg') }}" alt="" style="width: 24px; height: 24px;">
         Workflow Guide
     </h2>
-    <div style="margin-top: 1rem; padding: 1rem; background: #f8f9fa; border-radius: 4px;">
+    <div class="workflow-guide">
         <ol style="line-height: 2; margin: 0; padding-left: 1.5rem;">
             <li><strong>Create a Playlist</strong> - Group your content into themed collections</li>
             <li><strong>Upload Media</strong> - Add images, videos, or PDFs to your media library</li>
@@ -81,17 +81,49 @@
     </div>
 </div>
 
+<style>
+.workflow-guide {
+    margin-top: 1rem;
+    padding: 1rem;
+    background: #f8f9fa;
+    border-radius: 4px;
+    border: 1px solid #e2e8f0;
+}
+
+body.dark-mode .workflow-guide {
+    background: #1a202c;
+    border: 1px solid #4a5568;
+}
+
+.secondary-text {
+    color: #7f8c8d;
+}
+
+body.dark-mode .secondary-text {
+    color: #a0aec0;
+}
+
+.log-item {
+    padding: 0.5rem;
+    border-bottom: 1px solid #e2e8f0;
+}
+
+body.dark-mode .log-item {
+    border-bottom: 1px solid #4a5568;
+}
+</style>
+
 {% if recent_logs %}
 <div class="card">
     <h2>Recent Activity</h2>
     <div style="margin-top: 1rem;">
         {% for log in recent_logs %}
-        <div style="padding: 0.5rem; border-bottom: 1px solid #eee;">
+        <div class="log-item">
             <span style="color: {% if log.level == 'error' %}#e74c3c{% elif log.level == 'warning' %}#f39c12{% else %}#27ae60{% endif %}; font-weight: bold;">
                 [{{ log.level.upper() }}]
             </span>
             {{ log.message }}
-            <small style="color: #7f8c8d; float: right;">{{ log.timestamp.strftime('%Y-%m-%d %H:%M:%S') }}</small>
+            <small class="secondary-text" style="float: right;">{{ log.timestamp.strftime('%Y-%m-%d %H:%M:%S') }}</small>
         </div>
         {% endfor %}
     </div>