fix: danmaku template now uses event rules; rules apply instantly on save

- _on_danmaku renders via event_text(rules, 'danmaku', ...) like all other
  events; hardcoded {uname}说、 {msg} format removed
- Drop message_format param from DanmakuHandler/DanmakuClient/server/main
- api_rules_post mutates the shared rules dict in place (clear+update)
  instead of rebinding, so running handlers pick up new templates
  immediately without restarting TTS
- UI save toast: '规则已保存并即时生效'
- Verified: custom template 卧槽！、是{uname}！、他说、 {msg} works;
  save-then-next-danmaku uses new template without restart

server.py

@@ -58,7 +58,6 @@ class TTSService:
             voice = config.get("voice", "f1")
             speed = config.get("speed", 100)
             self._volume = config.get("volume", 100)
-            message_format = config.get("format", "{uname}\u8bf4\u3001 {msg}")
             convert_numbers = config.get("convert_numbers", True)
             self.current_config = config
             self.recent_messages = []
@@ -71,7 +70,6 @@ class TTSService:
             self._danmaku_client = DanmakuClient(
                 room_id=room_id, queue=self._queue,
                 cookies=self._cookies, rules=event_rules,
-                message_format=message_format,
             )
             await self._danmaku_client.start()
             self.running = True
@@ -169,7 +167,6 @@ async def api_start(request: web.Request) -> web.Response:
     config.setdefault("voice", "f1")
     config.setdefault("speed", 100)
     config.setdefault("volume", 100)
-    config.setdefault("format", "{uname}\u8bf4\u3001 {msg}")
     config.setdefault("convert_numbers", True)
     if tts_service.running:
         try:
@@ -248,7 +245,6 @@ async def api_rules_get(request: web.Request) -> web.Response:
 
 
 async def api_rules_post(request: web.Request) -> web.Response:
-    global event_rules
     try:
         new_rules = await request.json()
     except Exception:
@@ -275,7 +271,11 @@ async def api_rules_post(request: web.Request) -> web.Response:
         save_rules(merged)
     except OSError as e:
         return web.json_response({"error": f"Failed to save rules: {e}"}, status=500)
-    event_rules = merged
+
+    # Mutate in place so running handlers (which hold the same dict reference)
+    # pick up the new rules immediately without restarting TTS.
+    event_rules.clear()
+    event_rules.update(merged)
     return web.json_response({"status": "saved", "rules": event_rules})