Log local sneak detection and proxy sneak observer

Add diagnostics and a log-only proxy observation for sneak state changes.

- docs/dev-log.md: Add entries documenting proxy sneak observation and local sneak detection diagnostics, scope notes, and next steps.
- plugin/src/main.cpp: Introduce SneakDetectionState, GetSneakDetectionState, and ShouldLogSneakDetection to combine API and actor-state signals; throttle diagnostic logs; use the combined finalIsSneaking in player movement state decisions; add include for ACTOR_STANCE.
- plugin/src/F4TProxyActorController.cpp: Add controller-local tracking for the represented remote player sneak state, reset helpers, and ApplyRemoteMovementStateToProxy which logs sneak transitions for the represented remote player (no visual crouch applied yet).

Notes: This change is log-only — it does not force animations or ActorState writes. Networking protocol and receive-thread behavior remain unchanged. A TODO is left to safely apply visual crouch once a supported API is confirmed.

docs/dev-log.md

@@ -761,6 +761,82 @@ Player position: X=2048.00, Y=2048.00, Z=0.00, AngleZ=0.00
 
 ---
 
+## 2026-06-02 - Proxy Sneak State Observation
+
+### What Changed
+
+- Added a log-only movement-state behaviour hook in `F4TProxyActorController`.
+- The single represented proxy now observes the remote player's `isSneaking`
+  value after the normal same-cell validation.
+- Added controller-local tracking for the represented remote `playerId` and its
+  last observed sneak state so logs happen only on transitions.
+- Reset sneak-state tracking when the represented remote player changes or
+  disappears.
+
+### What Worked
+
+- Existing smooth proxy transform movement remains unchanged.
+- Special movement types still snap through the existing movement path.
+- The networking receive thread remains actor-free and continues to update only
+  plain remote-player state.
+
+### What Broke
+
+- Nothing recorded.
+
+### Notes
+
+- This milestone intentionally does not force the proxy to crouch visually.
+- Animation graph variables/events, direct `ActorState` writes, and
+  `PerformAction(kActionSneak)` remain out of scope until a safe actor crouch API
+  is confirmed.
+- Dynamic spawning, multiple proxy actors, combat, inventory, quest, settlement,
+  weapon, and interaction sync remain out of scope.
+
+### Next Steps
+
+- Test with two Fallout 4 clients in `F4TTestCell01` and confirm sneak toggles
+  produce one log line per transition.
+- Research a safe visual crouch/sneak application path for the placed proxy
+  actor.
+
+---
+
+## 2026-06-02 - Local Sneak Detection Diagnostics
+
+### What Changed
+
+- Improved local `isSneaking` detection to combine safe read-only signals from
+  `PlayerCharacter::IsSneaking()`, actor-state stance, and actor-state
+  `forceSneak`.
+- Added throttled local sneak diagnostics showing each read-only signal and the
+  final `isSneaking` value sent in transform packets.
+- Kept movement-state change detection unchanged, so `isSneaking` transitions
+  can trigger transform sends even without a meaningful position delta.
+
+### What Worked
+
+- The networking protocol remains unchanged and backwards compatible.
+- The receive thread remains actor-free.
+- Proxy sneak behaviour remains log-only; no visual crouch is applied.
+
+### What Broke
+
+- Nothing recorded.
+
+### Notes
+
+- No animation graph variables/events, direct actor-state writes, or
+  `PerformAction(kActionSneak)` were added.
+- Server files and fake-client compatibility were left unchanged.
+
+### Next Steps
+
+- Test crouch/sneak in-game and compare `apiSneaking`, `actorStateSneaking`,
+  `actorStateForceSneak`, and `finalIsSneaking` in `Fallout4Together.log`.
+
+---
+
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