refactor(hooks): consolidate hooks.json description into ssot.json gate registry #1222

Facts

• hooks/hooks.json's top-level description field has grown into a single
  large run-on paragraph documenting the rationale for every hook ever
  added, citing issue numbers feat: re-run provenance/placeholder scan against the actually-posted PR/issue body (post-write verification) #878, feat(hooks): add PreToolUse hook to block issue creation without ACM disclosure #413, fix(gate-skill-audit-disclosure): close disclosure gaps in script + PR template #517, chore(retrospective): merge retrospective for PR #186 #187, refactor(skills): rename driving-pr-to-merge -> drafting-a-pr-to-merge; terminal state is DRAFT, never merge #637, feat(hooks): gate PR creation on referenced issue's ACM/waiver disclosure #657, Add a deterministic gate restricting PR titles to Conventional Commits format #1058, and
  fix(dedup): add deterministic duplicate-work checks for PRs, retrospective issues, and new issues #1197.
• This content duplicates what .gitapex/ssot.json's gates[] array already
  tracks per-gate, structured, in its own rule and tracking_issue fields
  -- confirmed directly by reading both files.
• Direct investigation: of the 10 hook scripts hooks/hooks.json wires, 9
  already have a corresponding .gitapex/ssot.json gate entry. Only
  hooks/check-merge-pull-request-block.sh (backing issue refactor(skills): rename driving-pr-to-merge -> drafting-a-pr-to-merge; terminal state is DRAFT, never merge #637) has none.
• No existing deterministic gate or test asserts on hooks.json's
  description field content -- confirmed by a repo-wide search.
  gitapex_gate_plugin_root_brace_notation.py explicitly scopes itself to
  command values only and states description: is never graded.
• .github/scripts/gitapex_gate_skill_audit_disclosure.py's own docstring
  confirms a diff touching both .gitapex/ssot.json and hooks/hooks.json
  (its own words: "the two files that decide whether gates run at all")
  requires a deterministic-gate-quality skill-audit disclosure on the PR
  that implements this.
• The repo owner directly requested this consolidation in this session's
  own conversation, after an earlier exchange establishing that hooks.json's
  description field was the source of the duplication.

Requested outcome

Shrink hooks/hooks.json's top-level description field to a short pointer
directing readers to .gitapex/ssot.json's gates[] registry as the single
source of truth for gate rationale, and register the one currently-missing
gate entry (hooks/check-merge-pull-request-block.sh, issue #637) so no
rationale is lost in the consolidation.

Acceptance Criteria Map

Draft, not pre-verified -- planning-a-branch-from-an-issue's own Step 4
independently re-checks each row against this issue's own stated facts
before implementation, rather than trusting it merely for being
well-formed.

Constraints

• No change to any hook's actual runtime behavior -- documentation/registry
  consolidation only.
• Every issue number currently named in hooks.json's own description must
  either already resolve inside .gitapex/ssot.json or be added by this
  same change -- nothing may simply disappear.

Non-goals

• Does not touch any other hooks.json field (command, timeout,
  matcher values) or any other existing .gitapex/ssot.json gate entry.
• Does not address the three sibling PreToolUse hooks' own jq-coalescing
  bug named as a follow-up in PR fix(dedup): add deterministic duplicate-work checks for PRs and issues #1215's own Risk/blast-radius section --
  that is separate, already-flagged follow-up work, out of this issue's
  scope.
• Does not extend to .github/workflows/*.yml files' own duplicated
  rationale prose -- that is issue CI gate workflows: centralize duplicated cross-workflow rationale prose into one shared reference doc #1186's own, distinct scope (see Dedup
  below).

Dedup

Dedup: search_issues query "consolidate hooks.json description into
ssot.json gate registry, remove duplicated rationale", 3 results reviewed
-- none duplicate this issue (detail below).

• CI gate workflows: centralize duplicated cross-workflow rationale prose into one shared reference doc #1186 (open) -- related in spirit (de-duplicating rationale prose) but a
  distinct scope: centralizing rationale repeated across multiple
  .github/workflows/*.yml files' own header comments into a new shared
  doc, not hooks/hooks.json's description field, and not consolidating
  into an already-existing structured registry. Not a duplicate; no fold-in.
• refactor(gates): extract shared JSON-schema load/validate helper #755 (closed) -- unrelated (a JSON-schema load/validate helper
  extraction).
• feat(cli): define .gitapex/ssot.json gate-registry schema (child of #82) #123 (closed) -- the original issue that specced .gitapex/ssot.json's
  own schema; this issue extends that registry, doesn't duplicate its
  creation.

Next Move

Draft ready to create as-is; no open question blocks filing it.