feat: add ws_base_url instance setting for WebSocket URL override (#8405)

* feat: add ws_base_url instance setting to override WebSocket base URL

Allow deployments behind reverse proxies to route WebSocket traffic
(LSP, debugger, multiplayer) to a different host/port than the main
frontend via a new instance setting.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: move ws_base_url to Advanced section with toggle and connectivity test

- Move setting from Core to Advanced > WebSocket section
- Render as toggle "Custom websocket base url from frontend to
  multiplayer/lsp/debugger" with conditional URL text field
- Add Test connectivity button (always visible) that checks HTTP health
  and WebSocket ping for all three services (LSP, Multiplayer, Debugger)
- Add /ws/ping and /ws/health endpoints to LSP service
- Add /ws_mp/health HTTP and __ping__ WS handlers to multiplayer service
- Add /ping WS handler to debugger service
- Add CORS headers to health endpoints for cross-origin testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: toggle enabled check and testWs promise resolution

- Fix enabled derived to check only for null (not empty string),
  otherwise the toggle never turns on since toggleEnabled sets ''
- Fix testWs onclose handler to resolve(false) so the promise
  doesn't hang if the server closes without sending a message

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: make connectivity test work with existing services

- HTTP test: accept plain text "ok"/"okay" (old services) in addition
  to JSON {"status": "ok"} (new services), reject HTML (SPA fallback)
- WS test: resolve on onopen (connection established) instead of
  waiting for a specific pong message, so the test works even with
  services that don't have the new /ping handler yet

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lsp/pyls_launcher.py

@@ -90,6 +90,26 @@ class MainHandler(web.RequestHandler):
     def get(self):
         self.write("ok")
 
+class HealthHandler(web.RequestHandler):
+    def set_default_headers(self):
+        self.set_header("Access-Control-Allow-Origin", "*")
+        self.set_header("Content-Type", "application/json")
+
+    def get(self):
+        self.write(json.dumps({"status": "ok", "service": "lsp"}))
+
+    def options(self):
+        self.set_status(204)
+        self.finish()
+
+class PingHandler(websocket.WebSocketHandler):
+    def open(self):
+        self.write_message(json.dumps({"type": "pong", "service": "lsp"}))
+        self.close()
+
+    def check_origin(self, origin):
+        return True
+
 if __name__ == "__main__":
     monaco_path = "/tmp/monaco"
     os.makedirs(monaco_path, exist_ok=True)
@@ -107,8 +127,10 @@ if __name__ == "__main__":
             (r"/ws/ruff", RuffLS),
             (r"/ws/deno", DenoLS),
             (r"/ws/go", GoLS),
+            (r"/ws/ping", PingHandler),
+            (r"/ws/health", HealthHandler),
             (r"/", MainHandler),
-            (r"/health", MainHandler),
+            (r"/health", HealthHandler),
         ]
     )
     app.listen(port, address="0.0.0.0")