fix: improve config schema and serve from docs site (#1248)

Fix idleTimeout description to document human-friendly formats (30s,
5m, 1h) alongside raw milliseconds. Add trailing newline. Serve the
schema from the docs app at agent-browser.dev/schema.json via a
prebuild copy step, and update all $schema URLs to use the stable
docs-hosted URL instead of raw GitHub.

agent-browser.schema.json

@@ -147,7 +147,7 @@
     },
     "idleTimeout": {
       "type": "string",
-      "description": "Auto-shutdown the daemon after N ms of inactivity (e.g., '60000')."
+      "description": "Auto-shutdown the daemon after inactivity (e.g., '30s', '5m', '1h', or raw milliseconds like '60000')."
     },
     "model": {
       "type": "string",
@@ -163,4 +163,4 @@
     }
   },
   "additionalProperties": true
-}
+}