docs: sentence-case sweep across 10 more pages

- tools/plugin: Package Entrypoints
- tools/code-execution: How To Use It
- tools/browser-linux-troubleshooting: Root Cause, Config Reference
- install/bun: Lifecycle Scripts
- nodes/audio: Mention Detection in Groups
- nodes/images: Inbound Media to Commands (Pi)
- platforms/android: Connection Runbook
- plugins/building-plugins: Beta Release Testing
- web/control-ui: Content Security Policy
- security/THREAT-MODEL-ATLAS: Framework Attribution

docs/plugins/building-plugins.md

@@ -288,7 +288,7 @@ surfaces, not as the default pattern for new third-party plugins.
 <Check>Tests pass (`pnpm test -- <bundled-plugin-root>/my-plugin/`)</Check>
 <Check>`pnpm check` passes (in-repo plugins)</Check>
 
-## Beta Release Testing
+## Beta release testing
 
 1. Watch for GitHub release tags on [openclaw/openclaw](https://github.com/openclaw/openclaw/releases) and subscribe via `Watch` > `Releases`. Beta tags look like `v2026.3.N-beta.1`. You can also turn on notifications for the official OpenClaw X account [@openclaw](https://x.com/openclaw) for release announcements.
 2. Test your plugin against the beta tag as soon as it appears. The window before stable is typically only a few hours.