v0.17.5 — Backlog checklists maintained as work progresses

Added

• Backlog checklists are now maintained as work progresses (skills/common/backlog-checklists.md,
  new shared contract). The backlog family advanced status labels, progress comments and the
  manifest, but nothing ever flipped a markdown checkbox on the tracked items — and GitLab/GitHub
  render a task list as a progress counter, so a delivered Issue left its acceptance criteria and its
  box in the parent's task list unticked, under-reporting real progress to everyone reading the Epic.
  Two checklists, each with one exclusive owner:

  • Child task list (Epic ## Sub-Epics, Sub-Epic ## Issues) → /architect:merge-issue, and
    only when that child actually reaches done, since merging is what establishes it.
  • Acceptance criteria (Issue ## Acceptance Criteria) → /architect:implement-backlog
    (implemented) then /architect:review-issue (verified).

  Rules the whole family follows: tick on evidence, never on intent; edit the body in place,
  flipping only the [ ] → [x] marker (never regenerate a body from backlog-manifest.json, which
  would discard human edits); idempotent re-runs; unticking allowed when a review or revert disproves
  a criterion, with a stated reason; skip entirely on the GitLab native-Epic / GitHub sub-issue path,
  where the parent carries links instead of a task list; --dry-run edits no body.

Changed

• /architect:export-backlog authors both checklists as unticked - [ ] boxes — one per
  criterion, one per child — and ticks nothing itself. A Given/When/Then scenario now goes inside a
  single box: a criterion written as prose can never be ticked by the downstream skills.
• /architect:implement-backlog (Step 7) ticks the acceptance criteria its committed code
  satisfies (commit/test/doc as evidence) and names every box it left unticked in the same progress
  comment. It leaves the parent's task list alone — an Issue is not done until its PR/MR merges.
• /architect:review-issue (Step 5) reconciles the checklist against the review verdict before
  raising the PR/MR: confirmed criteria ticked, refuted ones unticked with the reason on the Issue,
  and anything still open surfaced in the PR/MR body.
• /architect:merge-issue reports unticked acceptance criteria at the Step 2 confirmation
  gate — deliberately not as a preflight check, so the "every preflight must pass" invariant stays
  absolute — and Step 4 ticks the Issue's box in its Sub-Epic, plus the Sub-Epic's box in the Epic
  when that Sub-Epic completes. Criteria the user waived are recorded in the merge comment, never
  ticked to look complete.
• /architect:deliver-backlog states that checkboxes are output, not resume input: stage
  selection still reads impl.status and the tracker labels, and a mismatched box is a defect for
  the owning skill to fix.