feat: add SEO audit support

skills/seo/SKILL.md

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+---
+name: seo
+description: Audit, plan, and implement SEO improvements across technical SEO, on-page optimization, structured data, Core Web Vitals, and content strategy. Use when the user wants better search visibility, SEO remediation, schema markup, sitemap/robots work, or keyword mapping.
+origin: ECC
+---
+
+# SEO
+
+Improve search visibility through technical correctness, performance, and content relevance, not gimmicks.
+
+## When to Use
+
+Use this skill when:
+- auditing crawlability, indexability, canonicals, or redirects
+- improving title tags, meta descriptions, and heading structure
+- adding or validating structured data
+- improving Core Web Vitals
+- doing keyword research and mapping keywords to URLs
+- planning internal linking or sitemap / robots changes
+
+## How It Works
+
+### Principles
+
+1. Fix technical blockers before content optimization.
+2. One page should have one clear primary search intent.
+3. Prefer long-term quality signals over manipulative patterns.
+4. Mobile-first assumptions matter because indexing is mobile-first.
+5. Recommendations should be page-specific and implementable.
+
+### Technical SEO checklist
+
+#### Crawlability
+
+- `robots.txt` should allow important pages and block low-value surfaces
+- no important page should be unintentionally `noindex`
+- important pages should be reachable within a shallow click depth
+- avoid redirect chains longer than two hops
+- canonical tags should be self-consistent and non-looping
+
+#### Indexability
+
+- preferred URL format should be consistent
+- multilingual pages need correct hreflang if used
+- sitemaps should reflect the intended public surface
+- no duplicate URLs should compete without canonical control
+
+#### Performance
+
+- LCP < 2.5s
+- INP < 200ms
+- CLS < 0.1
+- common fixes: preload hero assets, reduce render-blocking work, reserve layout space, trim heavy JS
+
+#### Structured data
+
+- homepage: organization or business schema where appropriate
+- editorial pages: `Article` / `BlogPosting`
+- product pages: `Product` and `Offer`
+- interior pages: `BreadcrumbList`
+- Q&A sections: `FAQPage` only when the content truly matches
+
+### On-page rules
+
+#### Title tags
+
+- aim for roughly 50-60 characters
+- put the primary keyword or concept near the front
+- make the title legible to humans, not stuffed for bots
+
+#### Meta descriptions
+
+- aim for roughly 120-160 characters
+- describe the page honestly
+- include the main topic naturally
+
+#### Heading structure
+
+- one clear `H1`
+- `H2` and `H3` should reflect actual content hierarchy
+- do not skip structure just for visual styling
+
+### Keyword mapping
+
+1. define the search intent
+2. gather realistic keyword variants
+3. prioritize by intent match, likely value, and competition
+4. map one primary keyword/theme to one URL
+5. detect and avoid cannibalization
+
+### Internal linking
+
+- link from strong pages to pages you want to rank
+- use descriptive anchor text
+- avoid generic anchors when a more specific one is possible
+- backfill links from new pages to relevant existing ones
+
+## Examples
+
+### Title formula
+
+```text
+Primary Topic - Specific Modifier | Brand
+```
+
+### Meta description formula
+
+```text
+Action + topic + value proposition + one supporting detail
+```
+
+### JSON-LD example
+
+```json
+{
+  "@context": "https://schema.org",
+  "@type": "Article",
+  "headline": "Page Title Here",
+  "author": {
+    "@type": "Person",
+    "name": "Author Name"
+  },
+  "publisher": {
+    "@type": "Organization",
+    "name": "Brand Name"
+  }
+}
+```
+
+### Audit output shape
+
+```text
+[HIGH] Duplicate title tags on product pages
+Location: src/routes/products/[slug].tsx
+Issue: Dynamic titles collapse to the same default string, which weakens relevance and creates duplicate signals.
+Fix: Generate a unique title per product using the product name and primary category.
+```
+
+## Anti-Patterns
+
+| Anti-pattern | Fix |
+| --- | --- |
+| keyword stuffing | write for users first |
+| thin near-duplicate pages | consolidate or differentiate them |
+| schema for content that is not actually present | match schema to reality |
+| content advice without checking the actual page | read the real page first |
+| generic “improve SEO” outputs | tie every recommendation to a page or asset |
+
+## Related Skills
+
+- `seo-specialist`
+- `frontend-patterns`
+- `brand-voice`
+- `market-research`