docs: add Local SEO skill reference

[cablate]

Summary

• New skills/google-maps/references/local-seo.md — teaches AI agents how to use geo tools for Local SEO / Google Business Profile ranking analysis
• 5-layer analysis model: keyword landscape → competitor deep dive → gap analysis → area density → monitoring
• 3 scenario recipes: full competitor audit (8-10 calls), quick rank check (2 calls), new location scouting (4 calls)
• Updated SKILL.md reference table, README project structure + use cases (EN/ZH)

Test plan

• Tested Scenario A (quick rank check) — 2 calls, results matched expectations
• Tested Scenario B (full competitor audit) — 8 calls, within 8-10 range
• Tested Scenario C (new location scouting) — 4 calls, density analysis accurate
• Edge case documented: maps_search_nearby keyword doesn't support Chinese category names

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