Add COVault109 solo-cell handling

Implement solo-cell logic to suppress transform packet sends and remote proxy representation while the local player is in COVault109, allowing first-time character creation to remain visually single-player. One entry location update is sent so other clients can hold stale proxies before suppression begins. Added F4TSoloCell.h helper for load-order-independent solo cell recognition by editor ID and cached FormID.

protocol/player-sync.md

@@ -31,6 +31,13 @@ Fallout 4 actors or references. If a remote player is not in the same
 cell/worldspace, the controller holds that player's proxy at a hidden in-cell
 position instead of leaving it at the last visible location.
 
+`COVault109` is treated as a solo cell for the first-time character-creation
+flow. On entry the plugin can send one location update so other clients hold any
+stale proxy, then it suppresses outgoing transform packets while the local
+player remains inside and the proxy controller skips remote representation. This
+is a client-side visibility/isolation rule and does not change the transform
+packet schema.
+
 ## Current Remote Player State Model
 
 The plugin and fake client store remote players by `playerId`.
@@ -97,6 +104,8 @@ player exists.
   resuming smoothing.
 - Transform packets include movement state data (`isMoving`, `movementSpeed`,
   `isSprinting`, `isSneaking`, `isJumping`, `weaponDrawn`).
+- The plugin suppresses transform sends and proxy representation in the
+  `COVault109` solo cell.
 - The game-thread proxy controller applies confirmed Havok animation graph
   variables to runtime proxy actors from that remote state (locomotion, sneak,
   jump, weapon drawn). Transform position/heading sync is unchanged.