feat(seo-skills): multi-backend Data Source Selection (#7)

Replaces single-vendor (Ahrefs-only) tool defaults with a per-task
backend menu across all 14 SEO skills. Each skill now lists every
capable MCP in allowed-tools and documents how to pick between
Semrush, Ahrefs, OurSEO Agent (CLI + MCP), DataForSEO, and GSC
in its SKILL.md Data Source Selection section.

Tool stubs (~40 new files) populated per skill with capability
deltas, call patterns, and explicit "not for this skill when"
callouts so the menu is self-correcting.

Skills affected: 19-keyword-strategy, 20-serp-analysis,
21-position-tracking, 22-link-building, 23-content-strategy,
24-ecommerce, 25-kpi-framework, 26-international, 27-ai-visibility,
28-knowledge-graph, 31-competitor-intel, 32-crawl-budget,
33-migration-planner, 34-reporting-dashboard.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/25-seo-kpi-framework/desktop/tools/ourseo.md

@@ -0,0 +1,38 @@
+# OurSEO Agent (CLI + MCP)
+
+In the KPI framework, OurSEO owns **technical health**, **indexed pages**, **GA4**, **GBP local**, and **first-party crawl-derived** KPIs. It is also the gateway to GSC via `our research search-console`.
+
+## KPI dimensions served by OurSEO
+
+| KPI | Command |
+|---|---|
+| Technical health score | `our audit tech https://<site>` |
+| Crawl efficiency / errors | `our analyze mysql-batch --session <id>` |
+| Indexed pages | `our research google index --domain <site>` / `mcp__ourseo__check_index` |
+| First-party clicks/impressions/CTR | `our research search-console queries --site sc-domain:<site> --days 28` |
+| GA4 sessions / traffic / channel | `our research ga4 traffic --property-id <id>` |
+| GA4 landing pages | `our research ga4 landing-pages --property-id <id>` |
+| GA4 channel mix | `our research ga4 channels --property-id <id>` |
+| GBP visibility / reviews / posts | `our collect gbp reviews/locations/posts ...`, `our audit local` |
+| Content freshness | `our collect crawl https://<site>` (extracts last-modified) |
+| Schema coverage | `our analyze mysql-batch --session <id> --export missing-schema` |
+
+## MCP equivalents (Claude Desktop)
+
+```
+mcp__ourseo__check_index(domain="<site>")
+mcp__ourseo__audit_page(url="<url>", audit_type="tech")
+mcp__ourseo__crawl_website(url="<site>", max_pages=100)
+```
+
+## Strengths for this skill
+
+- **First-party** GSC + GA4 + GBP all routed through one CLI — easiest way to get ground-truth KPIs.
+- **Owns technical health + indexed pages** end-to-end.
+- Stores results in MySQL workspace — supports period-over-period KPI comparison without re-pulling.
+
+## Not for this skill when
+
+- **Modelled traffic-value** — Semrush `overview_research` is the cleanest source.
+- **Backlinks / DR / Authority** — Ahrefs (or Semrush) backlink endpoints.
+- **AI visibility KPI** — Ahrefs Brand Radar.