refactor: remove standalone mode, consolidate to managed-only (PostgreSQL) (#70)

- Remove standalone mode code: file-based stores, standalone gateway,
  heartbeat service, SQLite memory, standalone docker-compose
- Rename docker-compose.managed.yml → docker-compose.postgres.yml
- Clean up ~130 Go comments referencing "managed mode" qualifier
- Simplify docker-compose.yml env vars (providers/channels via web UI)
- Update .env.example to essential vars only (token + encryption key)
- Add setup wizard UI (provider → agent → channel bootstrap flow)
- Add logs.tail WebSocket handler for live log streaming
- Add cursor-pointer to interactive UI components
- Clean up config page (remove standalone-only sections)
- Update README and docs for managed-only architecture

docs/01-agent-loop.md

@@ -171,8 +171,7 @@ The system prompt is assembled dynamically from 15+ sections. Two modes control
 13. **Extra context** -- additional prompt text wrapped in `<extra_context>` XML tags.
 14. **Project Context** -- context files loaded from the database or filesystem, wrapped in `<context_file>` XML tags with a defensive preamble.
 15. **Silent Replies** -- instructions for the NO_REPLY convention.
-16. **Heartbeats** -- instructions for periodic wake-up behavior.
-17. **Sub-Agent Spawning** -- rules for launching child agents.
+16. **Sub-Agent Spawning** -- rules for launching child agents.
 18. **Delegation** -- auto-generated `DELEGATION.md` listing available delegation targets (inline if ≤15, search instruction if >15).
 19. **Team** -- `TEAM.md` injected for team leads only (team name, role, teammate list).
 20. **Runtime** -- runtime metadata (agent ID, session key, provider info).