Add Layouts module with Konva.js builder; smart offline polling; UI improvements

- Move board cards from dashboard to top of boards list page
- Fix Werkzeug duplicate polling (WERKZEUG_RUN_MAIN guard)
- Smart offline polling: fast loop for online boards, slow recheck for offline
- Add manual ping endpoint POST /api/boards/<id>/ping
- Add spin animation CSS for ping button

Layouts module (new):
- app/models/layout.py: Layout model (canvas_json, thumbnail_b64)
- app/routes/layouts.py: 5 routes (list, create, builder, save, delete)
- app/templates/layouts/: list and builder templates
- app/static/js/layout_builder.js: full Konva.js builder engine
- app/static/vendor/konva/: vendored Konva.js 9
- Structure mode: wall, room, door, window, fence, text shapes
- Devices mode: drag relay/input/Sonoff channels onto canvas
- Live view mode: click relays/Sonoff to toggle, socket.io state updates
- Device selection: click to select, remove individual device, Delete key
- Fix door/Arc size persistence across save/reload (outerRadius, scaleX/Y)
- Fix Sonoff devices missing from palette (add makeSonoffChip function)

app/templates/layouts/list.html

@@ -0,0 +1,105 @@
+{% extends "base.html" %}
+{% block title %}Layouts – Location Management{% endblock %}
+
+{% block content %}
+<div class="d-flex align-items-center justify-content-between mb-4">
+  <h2 class="fw-bold mb-0"><i class="bi bi-map me-2 text-info"></i>Layouts</h2>
+  {% if current_user.is_admin() %}
+  <button class="btn btn-primary" data-bs-toggle="modal" data-bs-target="#newLayoutModal">
+    <i class="bi bi-plus-circle me-1"></i> New Layout
+  </button>
+  {% endif %}
+</div>
+
+{% if layouts %}
+<div class="row g-3">
+  {% for layout in layouts %}
+  <div class="col-sm-6 col-xl-4">
+    <div class="card border-0 rounded-4 h-100">
+      <!-- thumbnail or placeholder -->
+      <div class="rounded-top-4 overflow-hidden d-flex align-items-center justify-content-center bg-dark"
+           style="height:180px">
+        {% if layout.thumbnail_b64 %}
+        <img src="{{ layout.thumbnail_b64 }}" alt="thumbnail"
+             style="max-width:100%;max-height:100%;object-fit:contain" />
+        {% else %}
+        <i class="bi bi-map display-1 text-secondary opacity-25"></i>
+        {% endif %}
+      </div>
+      <div class="card-body">
+        <h5 class="fw-semibold mb-1">{{ layout.name }}</h5>
+        {% if layout.description %}
+        <p class="text-secondary small mb-0">{{ layout.description }}</p>
+        {% endif %}
+      </div>
+      <div class="card-footer bg-transparent d-flex justify-content-between align-items-center">
+        <span class="text-secondary small">
+          {% if layout.updated_at %}
+            Updated {{ layout.updated_at.strftime('%Y-%m-%d %H:%M') }}
+          {% else %}
+            Created {{ layout.created_at.strftime('%Y-%m-%d') }}
+          {% endif %}
+        </span>
+        <div class="d-flex gap-1">
+          <a href="{{ url_for('layouts.builder', layout_id=layout.id) }}"
+             class="btn btn-sm btn-outline-primary">
+            <i class="bi bi-pencil-square me-1"></i>Edit
+          </a>
+          {% if current_user.is_admin() %}
+          <form method="POST" action="{{ url_for('layouts.delete_layout', layout_id=layout.id) }}"
+                class="d-inline" onsubmit="return confirm('Delete layout \'{{ layout.name }}\'?')">
+            <button class="btn btn-sm btn-outline-danger"><i class="bi bi-trash"></i></button>
+          </form>
+          {% endif %}
+        </div>
+      </div>
+    </div>
+  </div>
+  {% endfor %}
+</div>
+{% else %}
+<div class="text-center py-5 text-secondary">
+  <i class="bi bi-map display-2 opacity-25"></i>
+  <p class="mt-3 fs-5">No layouts yet.</p>
+  {% if current_user.is_admin() %}
+  <button class="btn btn-primary" data-bs-toggle="modal" data-bs-target="#newLayoutModal">
+    <i class="bi bi-plus-circle me-1"></i> Create your first layout
+  </button>
+  {% endif %}
+</div>
+{% endif %}
+
+<!-- ── New layout modal ───────────────────────────────────────────────────── -->
+{% if current_user.is_admin() %}
+<div class="modal fade" id="newLayoutModal" tabindex="-1">
+  <div class="modal-dialog">
+    <form method="POST" action="{{ url_for('layouts.create_layout') }}">
+      <div class="modal-content">
+        <div class="modal-header border-0">
+          <h5 class="modal-title"><i class="bi bi-map me-2 text-info"></i>New Layout</h5>
+          <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
+        </div>
+        <div class="modal-body">
+          <div class="mb-3">
+            <label class="form-label">Name <span class="text-danger">*</span></label>
+            <input type="text" class="form-control" name="name" required maxlength="128"
+                   placeholder="e.g. Ground Floor, Garden" autofocus />
+          </div>
+          <div class="mb-3">
+            <label class="form-label text-secondary">Description <span class="text-secondary small">(optional)</span></label>
+            <input type="text" class="form-control" name="description" maxlength="256"
+                   placeholder="Short description" />
+          </div>
+        </div>
+        <div class="modal-footer border-0">
+          <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Cancel</button>
+          <button type="submit" class="btn btn-primary">
+            <i class="bi bi-arrow-right-circle me-1"></i>Create & Open Builder
+          </button>
+        </div>
+      </div>
+    </form>
+  </div>
+</div>
+{% endif %}
+{% endblock %}