chore(skill): bump to v3.1.0 + changelog

Minor bump because the changes since v3.0.7 are genuinely additive:

- Native subagent cross-compile pipeline and the Codex
  impeccable_asset_producer agent (Codex-only by design).
- Critique persistence: per-target snapshots, ignore.md, polish
  reads matching snapshot as additional signal.
- Codex-specific image flow extracted to reference/codex.md with
  the palette-first gate; craft.md is leaner for non-Codex.
- Detector: body-text-viewport-edge rule (29 total),
  OKLCH/var-resolution and anchor-inherit FP fixes.
- Brand register: inverse test and cultural-symbol palette
  guardrail.
- Shape gates restored where weakening had crossed the line
  (image-gen announcement, explicit brief confirmation).

Hero version link and full-history block updated. Manifests and
harness SKILL.md frontmatter all on 3.1.0.

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

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "impeccable",
   "description": "Design fluency for frontend development. 1 skill with 23 commands (/impeccable polish, /impeccable audit, /impeccable critique, etc.) and curated anti-pattern detection.",
-  "version": "3.0.7",
+  "version": "3.1.0",
   "author": {
     "name": "Paul Bakaus",
     "email": "paul@paulbakaus.com"