feat: test coverage gate + plan completion audit + auto-verification

Three new gates in /ship and /review:
1. Test coverage gate: configurable thresholds (60%/80% default), hard stop
   below minimum with user override
2. Plan completion audit: discovers plan file, extracts actionable items,
   cross-references against diff, gates on NOT DONE items
3. Auto-verification: invokes /qa-only inline with plan's verification
   section, conditional on localhost reachability

Also: coverage warning in /review, plan completion data in /retro,
shared plan file discovery helper (DRY), ship metrics logging.

review/SKILL.md.tmpl

@@ -45,7 +45,10 @@ Before reviewing code quality, check: **did they build what was requested — no
    **If no PR exists:** rely on commit messages and TODOS.md for stated intent — this is the common case since /review runs before /ship creates the PR.
 2. Identify the **stated intent** — what was this branch supposed to accomplish?
 3. Run `git diff origin/<base> --stat` and compare the files changed against the stated intent.
-4. Evaluate with skepticism:
+
+{{PLAN_COMPLETION_AUDIT_REVIEW}}
+
+4. Evaluate with skepticism (incorporating plan completion results if available):
 
    **SCOPE CREEP detection:**
    - Files changed that are unrelated to the stated intent