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/services/board_service.py

@@ -84,14 +84,14 @@ def poll_board(app, board_id: int) -> None:
             "is_online": board.is_online,
             "relay_states": board.relay_states,
             "input_states": board.input_states,
+            "last_seen": board.last_seen.isoformat() if board.last_seen else None,
         })
 
 
-def poll_all_boards(app) -> None:
-    """Poll every registered board in parallel."""
-    with app.app_context():
-        board_ids = [r[0] for r in db.session.query(Board.id).all()]
-
+def _poll_boards_by_ids(app, board_ids: list) -> None:
+    """Spawn one thread per board_id and poll them in parallel."""
+    if not board_ids:
+        return
     threads = [
         threading.Thread(target=poll_board, args=(app, bid), daemon=True)
         for bid in board_ids
@@ -99,7 +99,30 @@ def poll_all_boards(app) -> None:
     for t in threads:
         t.start()
     for t in threads:
-        t.join(timeout=4)
+        t.join(timeout=6)
+
+
+def poll_online_boards(app) -> None:
+    """Poll only boards currently marked online (fast background loop)."""
+    with app.app_context():
+        board_ids = [
+            r[0] for r in db.session.query(Board.id).filter_by(is_online=True).all()
+        ]
+    _poll_boards_by_ids(app, board_ids)
+
+
+def recheck_offline_boards(app) -> None:
+    """Single-pass connectivity check for boards marked offline.
+
+    Called infrequently (default every 60 s) so we don't flood the network
+    with timeout requests for devices that are simply powered off.
+    Also triggered immediately when the user clicks 'Check Status'.
+    """
+    with app.app_context():
+        board_ids = [
+            r[0] for r in db.session.query(Board.id).filter_by(is_online=False).all()
+        ]
+    _poll_boards_by_ids(app, board_ids)
 
 
 # ── webhook registration ──────────────────────────────────────────────────────