Add match-start readiness barrier (Loading phase)

Gate the Lobby-to-world transition on a new MatchSubPhase.Loading before
Hide: movement stays frozen and the Hide countdown does not start until
every connected client has spawned all match avatars and applied their
paintings.

- MatchManager: Loading phase; matchLoadTimeout tunable; Match_BeginLoad
  broadcasts the respawned avatar NetworkObjectIds (+ generation tag),
  Match_Ready collects per-client ACKs (host self-checks locally); barrier
  coroutine in RunMatchPhases before Hide; disconnect/teardown cleanup.
- GameModeManager: freeze local player (movement/paint/tab) during Loading,
  restored via ActiveMode.Enter() on transition to Hide (no camera jump).
- NetworkPlayerSetup: treat Loading like Hide in ComputeVisible so a
  fast-loading client cannot reveal a hider early.
- MatchHud: "Loading" phase label.

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

Assets/Scripts/Network/NetworkPlayerSetup.cs

@@ -326,6 +326,9 @@ public class NetworkPlayerSetup : NetworkBehaviour
         if (role != PlayerRole.Hider) return true;     // hunters are always visible
 
         var phase = match.LocalSubPhase;
+        // The pre-match loading window conceals hiders exactly like Hide, so a fast-loading client can't reveal
+        // a hider (once its paint applies) before the match proper even begins.
+        if (phase == MatchManager.MatchSubPhase.Loading) phase = MatchManager.MatchSubPhase.Hide;
         if (phase == MatchManager.MatchSubPhase.Resolution) return true; // all revealed at the end
 
         if (match.LocalMatchMode == MatchManager.MatchMode.Conversion)