refactor: convert mac-optimizer from raw skill to proper plugin

Restructured 92-mac-optimizer from a CLAUDE.md-based skill into a full
Claude Code plugin with .claude-plugin/plugin.json, 6 slash commands
(/mac-doctor, /mac-packages, /mac-environment, /mac-security,
/mac-cleanup, /mac-resources), and auto-trigger SKILL.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

custom-skills/92-mac-optimizer/commands/mac-packages.md

@@ -0,0 +1,32 @@
+---
+allowed-tools: Bash(bash *audit_packages.sh*), Bash(brew *), Bash(npm *), Bash(pip *), Bash(nvm *), Bash(pyenv *)
+description: Audit package managers (Homebrew, npm, pip, pyenv) for outdated packages and issues
+---
+
+## Your task
+
+Audit all package managers on this Mac.
+
+### Step 1 — Run the audit
+
+```bash
+bash $CLAUDE_PLUGIN_ROOT/skills/mac-optimizer/scripts/audit_packages.sh
+```
+
+### Step 2 — Report
+
+Parse JSON output and present as a severity-ranked markdown table:
+
+| Severity | Finding | Recommended Action | Details |
+|---|---|---|---|
+
+### Step 3 — Ask for consent
+
+List available update actions grouped by risk. Ask which actions to perform.
+
+### Safety notes
+
+- `brew upgrade` is generally safe but can break projects pinned to specific versions
+- Global npm packages are version-independent from project dependencies
+- pip upgrades can break dependency chains — suggest `--dry-run` first
+- Only audit pyenv-managed environments (not system Python)