fix(bridge): rescope verify's push box to committed, and stop over-claiming PRECHECK coverage

[AdrianTheopold]

Two defects found by the 1.3.0 audit sweep but left out of it, because
neither is the "names one instance where it means a class" shape the
sweep was hunting.

1. templates/verify.md §5 shipped the box "All relevant commits pushed",
   which can never be truthfully ticked: verify runs at apply step 3 and
   the branch is pushed at step 6. Observed live — a real cycle left it
   unchecked and wrote a prose note explaining why. Rescoped to "All code
   changes committed", which is what schema.yaml's own check 5 asks for
   ("Confirm all code changes are committed (no unstaged files in the
   worktree)"), so template and instruction now agree. A note records why
   it is committed-not-pushed, so it does not get "helpfully" restored.

2. The schema description claimed "Each artifact / apply step verifies
   its required skills before invoking and surfaces a clear error if any
   are missing." The verify artifact's openspec-verify-change invoke has
   no availability PRECHECK — deliberately, since it has a documented
   manual fallback. A class claim with an instance implementation: the
   inverse of the audited shape, and the description is the first thing
   openspec schemas shows an adopter. Now scoped to Superpowers skills
   and names the exception. README:439 and the touchpoint table were
   already correct on this, so no doc change was needed.

VERSION 1.3.0 → 1.3.1 (prose/template corrections, no gate change).
Validated: openspec schema validate superpowers-bridge passes, and the
corrected description renders as intended in openspec schemas.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com