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

crates/skald-core/src/skald/bundles.rs

@@ -345,6 +345,7 @@ impl Conversation {
             std::path::PathBuf::from("/root"),
             Vec::new(),
             Vec::new(),
+            None,
         ));
 
         let manager = Arc::new(ChatSessionManager::new(