Prevent acceptance-criteria commands from mutating excluded files

[caoergou]

Spec ## Exclusions often list files like backend/uv.lock. However, acceptance criteria can run commands such as uv run --with pytest ..., which rewrite uv.lock. The agent then has to manually git checkout -- uv.lock to keep the commit clean.

Expected: either generate criteria with --frozen when possible, or the harness should automatically restore files listed in ## Exclusions after running acceptance criteria.

Related: #62

[caoergou]

Reopening with evidence from a real run: the fix (_restore_exclusions, verification.py:118) is in place and runs at the right time — but it has never restored anything, due to a template↔parser contract mismatch:

• The spec template emits prose bullets: - Do NOT modify `backend/pyproject.toml` or `backend/uv.lock`
• get_spec_exclusions (spec_queue.py:356) does item.strip().strip("")`, yielding the whole English sentence as a "pathspec".
• git ls-files -- "Do NOT modify ..." matches zero files → the restore is a silent no-op.

Observed result: a ±370-line uv.lock churn was committed in iteration 1 of a 5-spec run despite the exclusion being present in the spec.

Fix options (ideally both): (a) parser extracts every backtick-quoted token from a bullet; (b) spec lint enforces bare-path bullets. Plus upgrading restore to a hard gate check (git diff --name-only ∩ exclusions ≠ ∅ → fail/strip+warn) — tracked in #78 finding 2. A contract test between template output and parser input would have caught this class of bug; see the MockAdapter e2e proposal in #78.