Wire config agents through UI event sessions

[ishaan-berri]

Summary

• routes config-defined agent chat through /session and the existing UI /event stream
• translates Claude Agent SDK stream events into UI message, thinking, and tool parts
• removes the duplicate managed /logs public route and direct-run UI panel so the UI uses one event contract

Verification

• cargo fmt --check
• python3 scripts/check_code_size.py
• cargo check --all-targets --locked
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --locked
• npm --prefix src/ui run lint
• npm --prefix src/ui run build
• local proxy proof with mocked E2B: POST /session, POST /session/{id}/prompt_async, and GET /event?key=sk-local streamed text deltas, thinking deltas, tool updates, and session.idle with the same sessionID

Notes

• No real E2B or Anthropic credentials were used for the proof run.