Harden summary-doc manifest adapter edge cases

[the-sarge]

Context

PR #111 moved summary-doc discovery into the Evidence baseline checker and made the pre-Go CI classifier read a generated manifest adapter.

The RAS review loop for PR #111 ended clean under the configured gate policy, but left low/nit/info follow-ups that should not block the PR.

Follow-up work

• Add a cheap shape guard in scripts/classify-check-changes.sh so non-comment manifest entries must match docs/*.md; fail with status 2 on malformed entries.
• Make scripts/classify-check-changes.sh --list-summary-docs propagate summary_doc_refs failures explicitly instead of relying on set -e.
• Add shell tests for malformed manifest entries and explicit failure propagation.
• Add a short note or help text clarifying that tools/evidencebaseline --list-summary-docs is a maintainer dry-run/inspection companion to --write-summary-docs.

Evidence

RAS review-fix run: 20260614T204231-f0307881a12cf606d27b9ee5
PR: #111