fix(plugin): slim Claude Code install (291MB→770KB) + fix skills path

- Marketplace source moved from "./" to "./plugin", a thin generated
  subtree containing only the plugin manifest and the impeccable skill.
  Per-version plugin cache shrinks ~378× (~770 KB instead of ~291 MB),
  and the lockfile is no longer included in the source path so the
  cache extraction never runs bun install. (#107)
- skills field in plugin.json now ends with a trailing slash to match
  the documented schema (code.claude.com/docs/en/plugins-reference,
  every directory example uses ./path/). Three reporters converged on
  this fix because Claude Code's plugin loader skips command
  registration on some setups when the slash is missing. (#86)
- Anti-patterns maintenance agent moved out of .claude/agents/ into
  CLAUDE.md / AGENTS.md as concise inline guidance, since it is
  repo-internal dev workflow, not user-facing. The plugin was also
  the only place this agent was exposed to install users.
- Skills version bumped to 3.0.2 so existing users pick up the new
  install path on next /plugin update.
- Top-level harness directories (.claude/skills/, .cursor/skills/, ...)
  intentionally stay where they are; npx skills add reads them
  directly from the GitHub repo and that path is unaffected.

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

plugin/.claude-plugin/plugin.json

@@ -0,0 +1,12 @@
+{
+  "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": "3.0.2",
+  "author": {
+    "name": "Paul Bakaus",
+    "email": "paul@paulbakaus.com"
+  },
+  "homepage": "https://impeccable.style",
+  "repository": "https://github.com/pbakaus/impeccable",
+  "skills": "./skills/"
+}