fix(3566): emit canonical [features].hooks; recognize legacy codex_hooks as alias

Closes #3566

Codex itself marks codex_hooks as a legacy_key in
codex-rs/features/src/legacy.rs. The canonical current Codex feature flag
under [features] is hooks. The GSD installer was still writing codex_hooks
on every fresh install / reinstall, leaving deprecated config behind on
Codex CLI >= 0.130.0.

Introduces a canonical/legacy split in bin/install.js:

  CODEX_HOOKS_FEATURE_KEY = 'hooks'
  CODEX_HOOKS_FEATURE_LEGACY_KEYS = ['codex_hooks']
  isCodexHooksFeatureKey(key)  // recognizes canonical OR any legacy alias

Threaded through:

- ensureCodexHooksFeature(): emits canonical hooks; recognizes legacy
  codex_hooks; migrates legacy -> canonical in section, root-dotted, and
  block-fallback insertion paths.
- hasEnabledCodexHooksFeature(): accepts either canonical or legacy.
- stripCodexHooksFeatureAssignments(): strips either canonical or legacy
  during uninstall when GSD owns the line.
- rewriteTomlKeyLines(): now always uses the caller-supplied key instead
  of the parsed-record keyRaw. The old `match.keyRaw || key` fallback was
  the proximate reason the migration silently no-op'd — callers asking
  to rewrite a section line to `hooks` got back the legacy `codex_hooks`
  line because the parsed record carried keyRaw="codex_hooks".

The GSD_CODEX_HOOKS_OWNERSHIP_PREFIX audit-marker string is intentionally
unchanged so existing installs' ownership lines continue to round-trip.

Tests:
- New tests/bug-3566-codex-hooks-feature-canonical-key.test.cjs (6 cases):
  fresh install writes hooks; section-form legacy migrated; root-dotted
  legacy migrated; user-owned hooks preserved; uninstall removes
  GSD-owned canonical; uninstall preserves user-owned hooks.
- Pre-existing legacy-pinning behaviour-change updates land in this PR
  via the rewriteTomlKeyLines + ensureCodexHooksFeature edits; the
  bug-2760-codex-install-defensive and bug-3427-3433 suites pass on the
  new shape without further test edits because they assert behaviour
  (not the literal key name).

Docs:
- docs/ARCHITECTURE.md row for Codex notes [features].hooks (canonical,
  legacy codex_hooks recognized and migrated forward).
- docs/installer-migrations.md row updated to reflect canonical key
  and the new Codex 0.130.0 features.hooks compatibility sentinel.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -737,7 +737,7 @@ The migration-specific ownership and source snapshots live in
 | OpenCode | `~/.config/opencode` | `./.opencode` | `command/gsd-*.md` | `agents/gsd-*.md` | `opencode.json` or `opencode.jsonc`; no GSD hooks |
 | Kilo | `~/.config/kilo` | `./.kilo` | `command/gsd-*.md` | `agents/gsd-*.md` | `kilo.json` or `kilo.jsonc`; no GSD hooks |
 | Gemini CLI | `~/.gemini` | `./.gemini` | `commands/gsd/*.toml` | `agents/gsd-*.md` | `settings.json` feature flag, hooks, and statusline |
-| Codex | `~/.codex` | `./.codex` | `skills/gsd-*/SKILL.md` | `agents/` source markdown plus per-agent TOML | `config.toml` `[agents.gsd-*]`, `[features].codex_hooks`, and hook tables |
+| Codex | `~/.codex` | `./.codex` | `skills/gsd-*/SKILL.md` | `agents/` source markdown plus per-agent TOML | `config.toml` `[agents.gsd-*]`, `[features].hooks` (canonical; legacy alias `codex_hooks` is recognized and migrated forward on reinstall, #3566), and hook tables |
 | GitHub Copilot | `~/.copilot` | `./.github` | `skills/gsd-*/SKILL.md` and `copilot-instructions.md` | `.agent.md` files | No GSD hooks or statusline |
 | Antigravity | `~/.gemini/antigravity` | `./.agent` | `skills/gsd-*/SKILL.md` | `agents/gsd-*.md` | Gemini-style `settings.json` hook entries when installed by GSD |
 | Cursor | `~/.cursor` | `./.cursor` | `skills/gsd-*/SKILL.md` | `agents/gsd-*.md` | Rule references under `rules/`; no GSD hooks |