Release prep: skill v3.9.0, CLI v3.2.0

Bump skill 3.8.0 -> 3.9.0 (plugin.json, marketplace.json, plugin/ subtree,
regenerated provider harness output) and CLI 3.1.0 -> 3.2.0 (package.json).

Changelog (site/pages/changelog.astro):
- Skill v3.9.0: codex grid-background ban, /impeccable bolder design-system
  lock, critique sub-agent independence on non-Claude/Codex harnesses,
  bundled helpers under strict-permission harnesses, Codex hook manifest fix.
- CLI v3.2.0: codex-grid-background detector rule, external skills-symlink
  preservation on first install.

Also: gitignore nested hook.cache.json/hook.pending.json copies (anchored
patterns missed the generated harness dirs), and repoint CLAUDE.md/AGENTS.md
changelog docs at changelog.astro with concise, user-facing-only tone guidance.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "impeccable",
-  "version": "3.1.0",
+  "version": "3.2.0",
   "author": "Paul Bakaus",
   "description": "Design skills, commands, and anti-pattern detection for AI coding agents",
   "keywords": [