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)

config.py

@@ -14,8 +14,10 @@ class Config:
         f"sqlite:///{os.path.join(BASE_DIR, 'instance', 'location_mgmt.db')}"
     )
     SQLALCHEMY_TRACK_MODIFICATIONS = False
-    # How often (seconds) the board poller updates relay states in the background
+    # How often (seconds) the fast poller updates ONLINE boards
     BOARD_POLL_INTERVAL = int(os.environ.get("BOARD_POLL_INTERVAL", 10))
+    # How often (seconds) offline boards are rechecked to see if they came back
+    OFFLINE_RECHECK_INTERVAL = int(os.environ.get("OFFLINE_RECHECK_INTERVAL", 60))
     # Base URL this server is reachable at (boards will POST webhooks here)
     SERVER_BASE_URL = os.environ.get("SERVER_BASE_URL", "http://localhost:5000")