Checkpoint: pre-realignment working tree (Gym->GymSub repoint + SyntyWorld/PostFX re-enable, SampleScene removed, PostFX_Daylight retune, ai.assistant pkg re-added)

Baseline before the LANTERN realignment & purge (plan: one look, four scenes,
Bathynaut on the player). Gym.unity edits are operator-made in-editor.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Packages/manifest.json

@@ -1,6 +1,7 @@
 {
   "dependencies": {
     "com.coplaydev.unity-mcp": "https://github.com/CoplayDev/unity-mcp.git?path=/MCPForUnity#main",
+    "com.unity.ai.assistant": "2.14.0-pre.1",
     "com.unity.ai.inference": "2.6.1",
     "com.unity.ai.navigation": "2.0.13",
     "com.unity.charactercontroller": "1.4.2",