Add real-time radar feature for nearby objects

Browser can open a radar window per character that streams nearby
monsters, players, NPCs, portals, and other objects in real-time.
On-demand activation via start_radar/stop_radar commands through
the existing WebSocket command channel.

- Backend: nearby_objects event handler with in-memory cache and broadcast
- Frontend: canvas mini-map + entity list table in draggable window
- Radar button added to player list alongside Chat/Stats/Inventory/Char

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

main.py

@@ -981,6 +981,7 @@ live_snapshots: Dict[str, dict] = {}
 live_vitals: Dict[str, dict] = {}
 live_character_stats: Dict[str, dict] = {}
 live_equipment_cantrip_states: Dict[str, dict] = {}
+live_nearby_objects: Dict[str, dict] = {}
 
 # Shared secret used to authenticate plugin WebSocket connections (override for production)
 SHARED_SECRET = "your_shared_secret"
@@ -2677,6 +2678,13 @@ async def ws_receive_snapshots(
                         f"Invalid portal message format from {websocket.client}: missing required fields"
                     )
                 continue
+
+            if msg_type == "nearby_objects":
+                character_name = data.get("character_name")
+                if character_name:
+                    live_nearby_objects[character_name] = data
+                    await _broadcast_to_browser_clients(data)
+                continue
             # Unknown message types are ignored
             if msg_type:
                 logger.warning(
@@ -2691,6 +2699,7 @@ async def ws_receive_snapshots(
         for name in disconnected_names:
             plugin_conns.pop(name, None)
             live_equipment_cantrip_states.pop(name, None)
+            live_nearby_objects.pop(name, None)
 
         # Clean up any plugin registrations for this socket
         to_remove = [n for n, ws in plugin_conns.items() if ws is websocket]