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/models/layout.py

@@ -0,0 +1,27 @@
+"""Layout model – stores a floor-plan / property map with placed device widgets."""
+from datetime import datetime
+from app import db
+
+
+class Layout(db.Model):
+    __tablename__ = "layouts"
+
+    id          = db.Column(db.Integer, primary_key=True)
+    name        = db.Column(db.String(128), nullable=False)
+    description = db.Column(db.String(256), nullable=True)
+
+    # Custom JSON schema (not raw Konva JSON) so we stay schema-independent:
+    # {
+    #   "structure": [ {id, tool, x, y, w, h, rotation, text, points}, … ],
+    #   "devices":   [ {id, boardId, entityType, entityNum, x, y}, … ]
+    # }
+    canvas_json   = db.Column(db.Text, nullable=True)
+
+    # PNG data-url for thumbnail shown on the list page
+    thumbnail_b64 = db.Column(db.Text, nullable=True)
+
+    created_at = db.Column(db.DateTime, default=datetime.utcnow)
+    updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+
+    def __repr__(self):
+        return f"<Layout {self.name!r} id={self.id}>"