feat: add multi-map system with 4 distinct biomes, layouts, and multiplayer sync

- Introduce 4 playable map environments:
  * Meadow (Grüne Lichtung): Classic balanced S-curve path with lush grasslands, flowers, and standard obstacles
  * Desert (Sonnendünen): Winding dune trail with sandstone rocks, oasis palms, and scrub
  * Frostland (Frostgipfel): Icy serpentine path through snowfields with frost-covered pines and crystal rocks
  * Volcano (Lavabruch): Tight aggressive layout through dark obsidian/basalt with glowing magma streams and floating ember sparks
- Add comprehensive MapDef & MapTheme configuration for distinct waypoint routes, flying trajectories, biome color palettes, portal/keep styles, and obstacle densities
- Extend Canvas 2D renderer to dynamically adapt backgrounds, path texturing, portal effects, and procedurally drawn biome foliage/decorations per map
- Upgrade GameEngine with dynamic map loading, obstacle clearing logic, and per-map highscore persistence
- Implement multiplayer map synchronization in WebSocket server (set-map event), room state, and lobby UI allowing host map selection
- Update StartScreen and LobbyScreen components with interactive map selection cards and per-map highscore tracking
- Add automated test suites for map path integrity, determinism, playability, and room map protocol synchronization

src/components/EndOverlay.vue

@@ -4,7 +4,7 @@ import { engine } from '@/game/engine'
 import { mpgame } from '@/game/mpgame'
 
 function restart(): void {
-  engine.startGame(store.difficulty)
+  engine.startGame(store.difficulty, store.mapId)
 }
 
 function endless(): void {