fix: real listener restart + remove listen_port editing from UI

Reviewer concerns:
1. POST /api/proxy/restart only saved config (reload), did not restart
   the listener. Now it touches data/restart.signal; proxy watcher
   polls that file separately and force-restarts the listener even
   when config is unchanged.
2. Editing proxy.listen_port via UI could break Docker port mapping
   (compose publishes 25565:25565 only). UI now shows it read-only;
   README documents how to change it together with compose.

- proxy/main.py: ProxyState.check_restart_signal() + watcher uses it
- api/config_io.py: touch_restart_signal() helper
- api/routes/status.py: /api/proxy/restart -> touch_restart_signal()
- frontend Settings: disabled listen_port input + 프록시 재시작 button
- README + .gitignore updated

proxy/main.py

@@ -20,6 +20,7 @@ import config as cfg_mod
 from handshake import HandshakeError, parse_handshake, read_handshake_bytes
 
 LOG_DB = Path(os.environ.get("MC_LOG_DB", "/data/logs.db"))
+RESTART_SIGNAL = Path(os.environ.get("MC_RESTART_SIGNAL", "/data/restart.signal"))
 
 logging.basicConfig(
     level=logging.INFO,
@@ -76,10 +77,18 @@ def log_event(
 # ---------------------------------------------------------------------------
 # Runtime state
 # ---------------------------------------------------------------------------
+def _signal_mtime() -> float:
+    try:
+        return RESTART_SIGNAL.stat().st_mtime
+    except FileNotFoundError:
+        return 0.0
+
+
 class ProxyState:
     def __init__(self) -> None:
         self.cfg = cfg_mod.load()
         self.cfg_mtime = cfg_mod.mtime()
+        self.signal_mtime = _signal_mtime()
         self.listen_port: int = int(self.cfg["proxy"]["listen_port"])
 
     def allowed(self) -> set[str]:
@@ -110,6 +119,15 @@ class ProxyState:
             log.warning("config reload failed: %s", exc)
             return False
 
+    def check_restart_signal(self) -> bool:
+        """`POST /api/proxy/restart` 가 touch 한 신호 파일 변경 여부."""
+        m = _signal_mtime()
+        if m == self.signal_mtime:
+            return False
+        self.signal_mtime = m
+        log.info("restart signal received")
+        return True
+
 
 # ---------------------------------------------------------------------------
 # TCP tunneling
@@ -249,11 +267,16 @@ async def config_watcher(state: ProxyState, listener: Listener) -> None:
         await asyncio.sleep(2)
         old_port = state.listen_port
         old_enabled = state.enabled()
-        if not state.reload_if_changed():
-            continue
+        config_changed = state.reload_if_changed()
+        signal_changed = state.check_restart_signal()
+
         new_port = int(state.cfg["proxy"]["listen_port"])
         new_enabled = state.enabled()
-        if new_port != old_port or new_enabled != old_enabled:
+
+        port_or_enabled_changed = (
+            config_changed and (new_port != old_port or new_enabled != old_enabled)
+        )
+        if signal_changed or port_or_enabled_changed:
             state.listen_port = new_port
             await listener.restart()