feat(web): show swarm agent status in chat

[BillDin]

Summary

• Bridge swarm runtime events into the session SSE stream so chat can show live per-agent status.
• Add an inline chat SwarmStatusCard with frontend state hydration from live events and final run_swarm results.
• Fix the Vite dev proxy default to 127.0.0.1 to avoid Windows localhost resolving to ::1 while the API binds IPv4.

Why

The terminal swarm dashboard already shows each agent's waiting/running/done/failed/blocked/retry state, but the web chat only showed the top-level run_swarm tool as a long-running tool. This PR brings the same status visibility into the chat timeline and keeps the existing swarm page/API wire shape intact.

Changes

• Inject the session event callback into SwarmTool and emit swarm.started / swarm.event frames through session SSE without changing /swarm/runs or /swarm/runs/{id}/events.
• Add SwarmRunStatus / SwarmAgentStatus frontend types, a swarm event reducer, and an inline SwarmStatusCard in the chat timeline.
• Hydrate a completed/failed card from the final run_swarm tool result for reconnect/history scenarios.
• Add focused frontend coverage for status rendering and event normalization.
• Default the frontend dev proxy to http://127.0.0.1:8899.

Test Plan

• Existing tests pass (pytest --ignore=agent/tests/e2e_backtest --tb=short -q)
  • Ran .venv\Scripts\python.exe -m pytest --ignore=agent/tests/e2e_backtest --ignore=agent/tests/test_e2e_harness_v2.py --tb=short -q: 3057 passed, 2 skipped; 6 failed and 9 errored due to local Windows-only environment issues outside this change: symlink privilege errors in agent/tests/factors/test_registry.py, Windows chmod mode assertions in agent/tests/test_oauth_token_cache.py, and cache-home path expectations in agent/tests/test_loader_retry_helpers.py.
• New tests added (if applicable)
  • .venv\Scripts\python.exe -m pytest agent/tests/test_swarm_status_hydration.py agent/tests/test_swarm_worker_report.py -q (32 passed)
  • cd frontend && npm run test:run -- SwarmStatusCard (5 passed)
• Tested manually (describe below)
  • cd frontend && npm run build passed.
  • Manual local smoke: backend health and Vite proxy were checked after changing the dev proxy default to 127.0.0.1.

Checklist

• No changes to protected areas (src/agent/, src/session/, src/providers/) without prior discussion
• No hardcoded values (API keys, file paths, magic numbers)
• Code follows CONTRIBUTING.md guidelines
• Documentation updated (not applicable: chat UI behavior is covered by tests and no docs page currently describes chat status cards)

[warren618]

Merged — really nice work. Bridging runtime events into the session SSE stream without changing the /swarm/runs shape was the right call, and rehydrating a finished card from the final run_swarm result covers the reconnect/history path cleanly. Appreciate the focused tests on both the live-event and no-session cases. 🙏