Add an end-to-end Verify smoke matrix (5 agents x levels, cache-hit) from docs/TODO

[AdvancedUno]

Summary

The "Verify (end-to-end)" checklist in docs/TODO.md is still entirely unchecked. Turn it into automated smoke/regression tests so the full pipeline can't silently break.

Why it matters

The unit suite mocks the provider per-module, but nothing exercises the whole pipeline across all agents/levels as a regression guard. These checks were planned and never wired.

Current behavior

docs/TODO.md:67-70, all unchecked:

• smoke matrix: 5 agents × {intern, senior} on a bundled resume + a real GitHub user
• level calibration shifts expectations (intern vs senior; phd-applicant vs postdoc)
• prompt-cache hit on the 2nd run (usage.cache_read_input_tokens > 0)

Proposed change

• Add a mocked-provider smoke test that runs all five agents end-to-end and asserts a well-formed Report, plus that changing --level shifts the level-expectation text in the prompt.
• Add a live, opt-in (env-gated) prompt-cache-hit assertion.

Acceptance criteria

• all-agents end-to-end smoke test (mocked provider) running in CI
• a level-calibration assertion
• a documented opt-in cache-hit check

---

Identified during a code review of the repo. Complements #11 (golden-fixture calibration harness): this issue is pipeline smoke/regression, #11 is scoring calibration.