feat(skill): refactor skill system with router + references structure (#192)

Refactors SKILL.md into a router + reference documentation system:
- Main SKILL.md now contains routing table and quick commands
- Detailed docs split into references/ (search, social, career, dev, web, video)
- CLI skill install copies entire directory including references/
- Resolves conflicts with recent merges (#210, #213)
- Fixes xreach→bird in quick commands

Original PR by @Citrus086, merged with conflict resolution.

Co-Authored-By: Citrus086 <Citrus086@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent_reach/skill/references/career.md

@@ -0,0 +1,29 @@
+# 职场招聘
+
+LinkedIn。
+
+## LinkedIn
+
+```bash
+# 获取个人资料
+mcporter call 'linkedin-scraper.get_person_profile(linkedin_url: "https://linkedin.com/in/username")'
+
+# 搜索人才
+mcporter call 'linkedin-scraper.search_people(keyword: "AI engineer", limit: 10)'
+
+# 获取公司资料
+mcporter call 'linkedin-scraper.get_company_profile(linkedin_url: "https://linkedin.com/company/xxx")'
+
+# 搜索职位
+mcporter call 'linkedin-scraper.search_jobs(keyword: "software engineer", limit: 10)'
+```
+
+> **需要登录**: LinkedIn scraper 需要有效的登录态。
+
+### Fallback 方案
+
+如果 MCP 不可用，可以用 Jina Reader：
+
+```bash
+curl -s "https://r.jina.ai/https://linkedin.com/in/username"
+```