Add lobby/match-start matchmaking flow with additive scene management

Replace the connection-approval role selection with a server-authoritative
match flow built on NGO additive scene management:

- Scenes: Main is the persistent foundation (NetworkManager, GameModeManager,
  cameras, HUD); Lobby and Test Map load/unload additively. Add Lobby + Test Map
  to the build settings; remove the obsolete SampleScene.
- MatchManager (plain MonoBehaviour singleton): loads Lobby on server start,
  StartMatchTrigger lets the host start the match, rolls one random Hunter (rest
  Hider), swaps Lobby -> Test Map (strictly serialized per NGO), respawns each
  player as its role variant. Forces additive client sync mode so clients keep
  Main instead of single-loading it (fixes "Destination scene is not valid").
- Server-driven spawning: null out NetworkConfig.PlayerPrefab at runtime to
  disable auto-spawn, then spawn players after the lobby floor exists (fixes
  falling through the floor) with double-spawn and transition guards.
- StartMatchTrigger: server-gated OnTriggerEnter, only the host's own player
  starts the match.
- NetworkBootstrap: drop role selection / connection approval; everyone spawns
  as the neutral Player prefab. Host/Client/Server/Shutdown buttons stay.
- NetworkPlayerSetup.ScopedModes flag (baked on Hunter/Hider prefabs): lobby
  avatar gets the full mode set, match variants get the role-scoped set.
- GameModeManager.BindLocalPlayer reads ScopedModes and rebinds the painter
  unconditionally (fixes stale painter binding on respawn -> brush painting in
  every mode).
- MeshPainter.PaintingEnabled defaults to false (unbound/pre-spawn/remote never
  paints); PaintHud visibility now also gates on a bound painter (fixes the HUD
  showing at startup before any avatar exists).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/GameModeManager.cs

@@ -137,8 +137,12 @@ public class GameModeManager : MonoBehaviour
         if (!localPlayer) return;
         player = localPlayer;
 
-        // The painter lives on the player (per-avatar), so bind the local one.
-        if (!painter) painter = localPlayer.GetComponentInChildren<MeshPainter>(true);
+        // The painter lives on the player (per-avatar), so bind the local one - UNCONDITIONALLY. On a
+        // lobby->match respawn the previous avatar is despawned and the role variant spawned in the same
+        // server frame; the old painter is Destroy-pending (still non-null) when this runs, so a
+        // `if (!painter)` guard would keep the stale reference and the new avatar's painter would never be
+        // mode-toggled - it would paint in every mode. Always re-point to the freshly spawned avatar.
+        painter = localPlayer.GetComponentInChildren<MeshPainter>(true);
         PainterChanged?.Invoke(painter);
 
         Transform camTarget = localPlayer.transform.Find("CameraTarget");
@@ -157,11 +161,16 @@ public class GameModeManager : MonoBehaviour
         ActiveMode?.Exit();
         _activeIndex = -1;
 
+        // Lobby/neutral avatar (base Player prefab) -> full mode set; match avatar (Hunter/Hider
+        // variant) -> only its role's modes. Baked per prefab, so no replicated-phase timing race.
         var setup = localPlayer.GetComponent<NetworkPlayerSetup>();
-        PlayerRole role = setup ? setup.Role : PlayerRole.Hider;
-        BuildModes(role);
+        if (setup && setup.ScopedModes)
+            BuildModes(setup.Role);
+        else
+            BuildModes(null);
 
-        // Each role list is ordered so index 0 is its start mode (Hunter -> First Person, Hider -> Player Control).
+        // Role lists are ordered so index 0 is the start mode (Hunter -> First Person, Hider -> Player
+        // Control); the full lobby set starts at Player Control too.
         SwitchTo(0);
     }