fix: close the four defects feedback issue #194 reported in code-review and research

[mxriverlynn]

Feedback issue #194 reported four runs where a Han skill confirmed a reference existed without confirming it pointed at the right thing, or produced a complete-looking report without saying what it had not done. Three were in code-review and one in research. This change makes both skills say what they did not do, and check that a reference supports the thing it is attached to.

What changed:

• code-review gains a named manual-only mode, entered when the dispatch mechanism fails (not when an agent returns nothing). The manual review sweeps mapped checklist categories in the absent agents' place, the report gains a ## Review Coverage section that renders only when coverage was absent, and the closing message names the cause and the count. The independent validation pass skips in that mode because it dispatches an agent.
• A Packaging (when applicable) checklist category fires on diffs that change what gets packaged. It raises a Warning saying the review did not open the built artifact and what to check by hand. Its summary row opens with Not checked —.
• A finding whose location came from a region read of a file over 1000 lines names its enclosing unit and the lines read to confirm it. Guarded twice: a fifth challenge axis in the validator brief, and a structural verification item that runs in every mode.
• research's traceability invariant is now two-part (resolvability and support), defined once in Operating Principles and cited elsewhere. The merge step records an old-to-new mapping across the renumbering, rewrites every citation surface through it including the evidence-status field, and labels a claim whose only source was dropped as no-evidence rather than single-source. Both inline column enumerations now name the one-line summary column.
• post-code-review-to-pr carries Review Coverage across to the pull request and exempts it from the clarity pass's length-matching, so the disclosure survives to the widest audience.
• Long-form docs for code-review, research, and post-code-review-to-pr updated to match.

The plan and its artifacts are under docs/plans/code-review-research-feedback-issue-194/. Two departures from the issue are recorded there as the operator's decision: the packaging finding discloses the gap rather than inspecting the artifact, and the location rule fires on the region-read path rather than on disassembler output the skill never reads.

Closes #194.