feat: port GaC-hkrpg-ps to Go with SceneCastSkill camera-detach fix

- mihoyo-variant KCP in pure Go (28-byte conv+token header), UDP gateway
  with 0xFF/0x145/0x194 handshake, ms-precision KCP clock + retransmit ticker
- protobuf for 4.6.51 generated from the AstralOS StarRail.proto (4932
  messages) plus CmdID map from // CmdID: comments (2114 ids)
- sdkserver port: query_dispatch/query_gateway (Gateserver pb + base64),
  hotfix fetch, auth endpoints, SRTools freesr-data.json upload
- gameserver handlers: login flow, scene load/spawn with real monster
  entity tracking, lineup, avatar/skin, missions, tutorials (1249+855),
  bag/equip, challenge incl. StartChallenge 1787 layout + Tierce 8973 +
  peak 8948, all raw tierce replies
- SceneCastSkill camera bug fix: only real scene monsters (tracked per
  session) trigger battle; attacking props/NPCs/air replies retcode 0
  without battle_info so the camera stays locked on the character
- end-to-end smoke test simulating a client over real UDP: handshake,
  PlayerGetToken, and both SceneCastSkill paths
- reuses the Rust PS data files unchanged (freesr-data.json, persistent,
  res.json, teleports.json, challenge_data.json, mission_unlocks.json)

internal/gameserver/handlers_avatar.go

@@ -0,0 +1,92 @@
+package gameserver
+
+import (
+	"gac-hkrpg-go/internal/common"
+	goproto "gac-hkrpg-go/protocol/proto"
+	"sort"
+)
+
+func init() {
+	handle("GetAvatarData", func(s *Session, req *goproto.GetAvatarDataCsReq, rsp *goproto.GetAvatarDataScRsp) error {
+		player := s.JSON()
+		if player == nil {
+			Log("data is not set!")
+			return nil
+		}
+
+		rsp.IsGetAll = req.IsGetAll
+
+		for _, id := range BaseAvatarIDs {
+			if av, ok := player.Avatars[id]; ok {
+				rsp.AvatarList = append(rsp.AvatarList,
+					av.ToAvatarProto(player.FindLightconeFor(id), player.MainCharacter.ID(), player.MarchType.ID()))
+			} else {
+				// avatar without save data: report a level-80 default
+				rsp.AvatarList = append(rsp.AvatarList, &goproto.Avatar{
+					BaseAvatarId:                id,
+					Level:                       80,
+					Promotion:                   6,
+					FirstMetTimestamp:           1712924677,
+					HasTakenPromotionRewardList: []uint32{1, 3, 5},
+				})
+			}
+		}
+
+		for _, av := range player.Avatars {
+			rsp.AvatarPathDataInfoList = append(rsp.AvatarPathDataInfoList,
+				av.ToAvatarPathDataProto(player.FindLightconeFor(av.AvatarID), player.FindRelicsFor(av.AvatarID), player.DressedSkins[av.AvatarID]))
+		}
+
+		// unlocked skins: res.json skinIds + currently dressed ones
+		seen := map[uint32]bool{}
+		for _, id := range player.DressedSkins {
+			if id != 0 && !seen[id] {
+				seen[id] = true
+				rsp.SkinList = append(rsp.SkinList, id)
+			}
+		}
+		if res, err := common.GameRes(); err == nil {
+			for _, id := range res.SkinIDs {
+				if id != 0 && !seen[id] {
+					seen[id] = true
+					rsp.SkinList = append(rsp.SkinList, id)
+				}
+			}
+		}
+		sort.Slice(rsp.SkinList, func(i, j int) bool { return rsp.SkinList[i] < rsp.SkinList[j] })
+
+		return nil
+	})
+
+	handle("DressAvatarSkin", func(s *Session, req *goproto.DressAvatarSkinCsReq, rsp *goproto.DressAvatarSkinScRsp) error {
+		player := s.JSON()
+		if player == nil {
+			return nil
+		}
+		player.DressedSkins[req.AvatarId] = req.AvatarSkinId
+		player.SavePersistent()
+		return nil
+	})
+
+	handle("TakeOffAvatarSkin", func(s *Session, req *goproto.TakeOffAvatarSkinCsReq, rsp *goproto.TakeOffAvatarSkinScRsp) error {
+		player := s.JSON()
+		if player == nil {
+			return nil
+		}
+		delete(player.DressedSkins, req.AvatarId)
+		player.SavePersistent()
+		return nil
+	})
+
+	handle("SetPlayerOutfit", func(s *Session, req *goproto.SetPlayerOutfitCsReq, rsp *goproto.SetPlayerOutfitScRsp) error {
+		return nil // retcode defaults to 0
+	})
+
+	handle("TakePromotionReward", func(s *Session, req *goproto.TakePromotionRewardCsReq, rsp *goproto.TakePromotionRewardScRsp) error {
+		return nil
+	})
+
+	handle("SetAvatarEnhancedId", func(s *Session, req *goproto.SetAvatarEnhancedIdCsReq, rsp *goproto.SetAvatarEnhancedIdScRsp) error {
+		return nil
+	})
+}