feat(sync): add install-skills.sh + install metadata to all 62 plugins

- Add install_name, install_type, dir_category fields to all 62 plugin.json files
  to resolve name-mapping and skill-vs-command routing issues
- Add install-skills.sh: idempotent cross-machine skill sync script
  - Routes skill→~/.claude/skills/<name>/, command→~/.claude/commands/<name>.md
  - rsync full skills/ directory (preserves multi-file skills like dev-test, req-deploy)
  - State file ~/.claude/.installed-skills.json tracks installed versions
  - Conflict detection: warns before overwriting locally modified files
  - --dry-run, --category, --force, --cleanup, --list flags
- Add 9 new plugins migrated from local ~/.claude (agent-swarm, ai-chat,
  defect-analysis, executing-plans, finishing-branch, frontend-design,
  req-audit, req-lookback, req-retro)
- Add update-plugin-meta.py helper used to bulk-update plugin.json
- Fix siyuan SKILL.md: remove hardcoded server credentials, use env vars

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

skills-biz/biz-contract-plugin/.claude-plugin/plugin.json

@@ -4,5 +4,8 @@
   "version": "1.0.0",
   "author": {
     "name": "qiudl"
-  }
+  },
+  "install_name": "biz-contract",
+  "install_type": "skill",
+  "dir_category": "biz"
 }