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)

cmd/gameserver/main.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+
+	"gac-hkrpg-go/internal/gameserver"
+)
+
+func main() {
+	fmt.Println("============================================================")
+	fmt.Println("  [GaC hkrpg GO] Gameserver (4.6.51) - ONLINE")
+	fmt.Println("  Listening on UDP port 23301 (KCP Gateway)")
+	fmt.Println("  Ready for StarRail client connection...")
+	fmt.Println("============================================================")
+
+	gw, err := gameserver.NewGateway("0.0.0.0", 23301)
+	if err != nil {
+		fmt.Println("failed to bind gateway:", err)
+		return
+	}
+	if err := gw.Listen(); err != nil {
+		fmt.Println("gateway error:", err)
+	}
+}

cmd/sdkserver/main.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"fmt"
+
+	"gac-hkrpg-go/internal/sdkserver"
+)
+
+func main() {
+	fmt.Println("============================================================")
+	fmt.Println("  [GaC hkrpg GO] SDK/Dispatch server - ONLINE")
+	fmt.Println("  Listening on HTTP port 21000")
+	fmt.Println("============================================================")
+
+	if err := sdkserver.Listen(); err != nil {
+		fmt.Println("sdkserver error:", err)
+	}
+}