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.

README.md

@@ -734,7 +734,7 @@ A [JSON Schema](agent-browser.schema.json) is available for IDE autocomplete and
 
 ```json
 {
-  "$schema": "https://raw.githubusercontent.com/vercel-labs/agent-browser/main/agent-browser.schema.json",
+  "$schema": "https://agent-browser.dev/schema.json",
   "headed": true
 }
 ```