feat: add dungeon map streaming and rendering in radar

- Backend: dungeon_map event handler with permanent in-memory cache
  by landblock ID, request_dungeon_map for late-joining browsers
- Frontend: render dungeon cells as colored rectangles when in dungeon,
  multi-level Z support (current floor bright, others dimmed),
  automatic overworld/dungeon switching based on is_dungeon flag,
  raw physics coordinate positioning for dungeon objects

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

main.py

@@ -982,6 +982,7 @@ live_vitals: Dict[str, dict] = {}
 live_character_stats: Dict[str, dict] = {}
 live_equipment_cantrip_states: Dict[str, dict] = {}
 live_nearby_objects: Dict[str, dict] = {}
+dungeon_map_cache: Dict[str, dict] = {}  # landblock hex string -> dungeon map data
 
 # Shared secret used to authenticate plugin WebSocket connections (override for production)
 SHARED_SECRET = "your_shared_secret"
@@ -2685,6 +2686,14 @@ async def ws_receive_snapshots(
                     live_nearby_objects[character_name] = data
                     await _broadcast_to_browser_clients(data)
                 continue
+
+            if msg_type == "dungeon_map":
+                landblock = data.get("landblock")
+                if landblock:
+                    dungeon_map_cache[landblock] = data
+                    logger.info(f"Cached dungeon map for {landblock} ({len(data.get('z_levels', []))} z-levels)")
+                    await _broadcast_to_browser_clients(data)
+                continue
             # Unknown message types are ignored
             if msg_type:
                 logger.warning(
@@ -2800,6 +2809,15 @@ async def ws_live_updates(websocket: WebSocket):
             except WebSocketDisconnect:
                 logger.info(f"Browser WebSocket disconnected: {websocket.client}")
                 break
+            # Handle dungeon map requests from browser
+            if data.get("type") == "request_dungeon_map":
+                landblock = data.get("landblock")
+                cached = dungeon_map_cache.get(landblock)
+                if cached:
+                    await websocket.send_json(cached)
+                    logger.debug(f"Sent cached dungeon map {landblock} to browser")
+                continue
+
             # Determine command envelope format (new or legacy)
             if "player_name" in data and "command" in data:
                 # New format: { player_name, command }