Bump all components 0.4.25 -> 0.4.26 and propagate via versions.json.

Ships the migration-gate fixes already on main:
- four-eyes plan-approval now reachable for RequiresReview schema diffs;
  Blocked always aborts; drop-unique honors allow_drop.
- udb plan/drift/manifest-export merge embedded native schemas like serve,
  so exported plans hash-match the serve-side diff.
- CI posture guards synced to the shipped bench/pages state.