feat: expose team specialists as top-level agents

[Mustafa-Esoofally]

Summary

• AgentOS previously only received teams=[coda], so the 5 specialists (Explorer, Researcher, Coder, Planner, Triager) were reachable only via team delegation and didn't appear in the AgentOS sidebar.
• Imports them from coda.agents.* and passes them directly to AgentOS(..., agents=[...]) alongside the existing teams=[coda].
• Each specialist stays as a member of the coda team, so delegation flows and share_member_interactions continue to work unchanged — they just become individually addressable as well.

Test plan

• Verified /config response on a local AgentOS boot (uvicorn app.main:app --port 8001) returns all 5 specialists under "agents" and coda still listed under "teams":
  ```
  "agents": [
  { "id": "explorer", "name": "Explorer", "db_id": "coda-db" },
  { "id": "researcher", "name": "Researcher", "db_id": "coda-db" },
  { "id": "coder", "name": "Coder", "db_id": "coda-db" },
  { "id": "planner", "name": "Planner", "db_id": "coda-db" },
  { "id": "triager", "name": "Triager", "db_id": "coda-db" }
  ]
  ```
• Slack interface still loads (the existing interfaces=[Slack(team=coda, ...)] wiring is untouched).
• After deploy: refresh os.agno.com and confirm the 5 specialists appear under AGENTS in the sidebar alongside the existing `coda` team entry.

Notes / Caveats

• `researcher` is `Optional[Agent]` in `coda/agents/researcher.py` — only constructed when `PARALLEL_API_KEY` is set. Railway already has this key, so prod is fine. If the key is ever removed, startup will `AttributeError` on `researcher.db` because `_initialize_agents` doesn't null-check. Kept the array plain (no filter) since `PARALLEL_API_KEY` is a hard requirement for Coda anyway.