0012 - add session API surface, docs, and CLI visibility

[ethanbailie]

This PR exposes session functionality to users through HTTP API, CLI config output, and docs, while preserving the core logic introduced in earlier stacked PRs.

What Changed

• API integration in tako_vm/server/app.py
  • app state now initializes/stops SessionManager in lifespan
  • added request/response models for sessions
  • added endpoints:
    • POST /sessions
    • GET /sessions
    • GET /sessions/{session_id}
    • POST /sessions/{session_id}/send
    • GET /sessions/{session_id}/events
    • POST /sessions/{session_id}/terminate
  • improved status typing reuse (SessionStatus alias from models)
• CLI updates in tako_vm/cli.py
  • show session settings in show-config
  • show per-job-type session/GPU details
• Added server export in tako_vm/server/__init__.py
• Documentation/examples updates:
  • README.md
  • docs/api/rest.md
  • docs/getting-started/configuration.md
  • docs/guide/environments.md
  • tako_vm.yaml.example

Tests Added/Updated

• tests/test_api.py
  • endpoint-level tests for session APIs
  • integration-style session API tests that use real SessionManager path with only subprocess boundary mocked
  • payload limit (413) verification
• tests/test_cli.py
  • confirms [Sessions] section and session/GPU job-type display

How To Review

1. Review endpoint contracts and error mapping in tako_vm/server/app.py.
2. Verify lifecycle wiring in app startup/shutdown.
3. Review tests/test_api.py:
   • first endpoint mapping tests
   • then integration-style session lifecycle tests for durability
4. Review CLI output and docs for consistency with API/config behavior.

Suggested Verification

• ruff check tako_vm tests
• pytest tests/test_api.py tests/test_cli.py -v

Out of Scope

• No new storage schema or manager core logic beyond prior PRs.
• No changes to GPU runtime policy beyond prior PRs.