Enhance map updates and component performance

- Updated API documentation to clarify the initial data message structure for real-time tile updates.
- Modified MapView component to load configuration and user data in parallel, improving map loading speed.
- Implemented asynchronous loading for markers after the map is visible, enhancing user experience.
- Introduced batching for tile updates to optimize rendering performance during map updates.
- Refactored character and marker creation functions to utilize dynamic Leaflet imports, improving modularity.

docs/api.md

@@ -60,7 +60,7 @@ The game client (e.g. Purus Pasta) communicates via `/client/{token}/...` endpoi
 
 ## SSE (Server-Sent Events)
 
-- **GET /map/updates** — real-time tile and merge updates. Requires a session with `map` permission. Sends `data:` messages with tile cache arrays and `event: merge` messages for map merges.
+- **GET /map/updates** — real-time tile and merge updates. Requires a session with `map` permission. Sends an initial `data:` message with an empty tile cache array `[]`, then incremental `data:` messages with tile cache updates and `event: merge` messages for map merges. The client requests tiles with `cache=0` when not yet in cache.
 
 ## Tile images