fix: update proxy path and MQTT broker URL in dev

Change the proxy path from `/journal` to `/.ttrpg` and ensure the
MQTT broker URL points to localhost:3000 during development to
match the CLI server configuration.

rsbuild.config.ts

@@ -46,7 +46,7 @@ export default defineConfig({
       "/__CONTENT_INDEX.json": "http://localhost:3000",
       "/__COMPLETIONS.json": "http://localhost:3000",
       "/content": "http://localhost:3000",
-      "/journal": "http://localhost:3000",
+      "/.ttrpg": "http://localhost:3000",
     },
   },
   output: {