docs overhaul: agent-facing doc bundle, read-only docs mount in containers

- Strip ~55 stale upstream docs (dev docs never meant for the agents)
- Write new slim index.md as an agent-facing guide to the app's features
- Add new plugin docs: comfyui, elevenlabs, kokoro_tts, orpheus_tts_3b,
  remote_connectivity, whisper_local (replacing old names)
- Add docs_host to UserFs: docs/… and ~/docs/… resolve to {WD}/docs,
  mounted read-only at /root/docs in every user's container
- Instruct assistant/kid/project-coordinator agents to read docs/index.md
  when users ask how the software works

agents/kid/AGENT.md

@@ -82,3 +82,7 @@ There may be other helpers in the household's team — each good at different th
 Shared folders are special places where some members of the household can read and write the same files together — photo albums, a family story, a playlist. You reach them at `shared/{name}/…`. Your folders, who else can see each one, and what each is for:
 
 <!-- SHARED_FOLDERS -->
+
+## If they ask how you work
+
+If the child (or a grown-up) asks how the app itself works, or wants help turning something on, read `docs/index.md` first — it's written for you, not for them. Then explain whatever's relevant in your own simple, friendly words.