Add complexionFormId to appearance payload

Introduce complexionFormId (TXST) into RemoteAppearance and the appearance protocol so complexion textures are captured and serialized. Updates: header/state, Networking JSON parse/serialize, proxy actor comparisons, main capture logic, protocol docs, fake client/player samples, changelog and dev-log. Capture reads PlayerCharacter::complexion and serializes it, but applying to proxies is intentionally a no-op because TESNPC proxies lack a complexion field (documented in comments/dev-log). Files: plugin/include/F4TRemotePlayerState.h, plugin/src/*, protocol/packets.md, server/fake_client.py, server/fake_player.py, changelog.md, docs/dev-log.md.

protocol/packets.md

@@ -81,6 +81,7 @@ Example after server processing:
     "bodyTintColor": { "r": 255, "g": 220, "b": 190, "a": 255 },
     "hairColorFormId": "",
     "facialHairColorFormId": "",
+    "complexionFormId": "",
     "headParts": [],
     "morphs": [],
     "morphRegions": [],
@@ -170,6 +171,7 @@ morphWeight           Body triangle weights: thin, muscular, and large.
 bodyTintColor         Body tint channels r, g, b, a as 0-255 integers.
 hairColorFormId       Hex-string `CLFM` form ID for hair color, or empty when unavailable.
 facialHairColorFormId Hex-string `CLFM` form ID for facial hair color, or empty when unavailable.
+complexionFormId      Hex-string `TXST` form ID for skin complexion (hands, arms, body tone), or empty when unavailable.
 headParts             Hex-string `HDPT` form IDs for the sender's current head parts.
 morphs                Morph slider values as `{ "id": hex-string, "value": number }` entries.
 morphRegions          Region morph slider values as a flat array of numbers (added in version 2).