feat: add local signup and Kakao verification gate

.env.example

@@ -28,6 +28,12 @@ GATEWAY_WORKSPACE_ROOT=/path/to/core2026
 GATEWAY_WORKTREE_ROOT=/path/to/core2026/.worktrees
 GATEWAY_USER_ICON_DIR=uploads/user-icons
 GATEWAY_USER_ICON_PUBLIC_URL=http://localhost:13000/user-icons
+GATEWAY_LOCAL_REGISTRATION_ENABLED=true
+GATEWAY_LOCAL_ACCOUNT_GRACE_DAYS=7
+# Optional. Keep the PEM private key outside Git; if omitted, a per-process RSA key is generated.
+# GATEWAY_PASSWORD_ENCRYPTION_PRIVATE_KEY_FILE=/run/secrets/gateway_password_private_key
+# Required only while imported ref SHA-512 credentials remain.
+# GATEWAY_LEGACY_PASSWORD_GLOBAL_SALT=replace-with-ref-global-salt
 SESSION_TTL_SECONDS=604800
 GAME_SESSION_TTL_SECONDS=21600
 OAUTH_SESSION_TTL_SECONDS=600