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/32-seo-crawl-budget/desktop/tools/ourseo.md

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+# OurSEO Agent (CLI + MCP)
+
+OurSEO contributes the **crawled URL inventory** (vs. server log observations), **index status check**, and **distributed crawl** for large sites. Pair with `scripts/log_parser.py` + `scripts/crawl_budget_analyzer.py` for the full crawl-budget picture.
+
+## CLI commands (Claude Code)
+
+```bash
+# URL inventory crawl
+our collect crawl https://<site> --max-pages 5000
+our collect crawl https://<site> --stealth --backend scrapy
+
+# Distributed crawl for large sites
+our collect distributed https://<site> --workers 8 --max-pages 50000
+
+# Index status (Google index coverage)
+our research google index --domain <site>
+
+# Technical audit (redirects, canonicals, etc.)
+our audit tech https://<site>
+
+# MySQL batch analysis on crawl results
+our analyze mysql-batch --session <id>
+our analyze mysql-batch --session <id> --export issues --format excel
+```
+
+## MCP tools (Claude Desktop)
+
+```
+mcp__ourseo__crawl_website(url="<site>", max_pages=5000)
+mcp__ourseo__check_index(domain="<site>")
+mcp__ourseo__audit_page(url="<url>", audit_type="tech")
+```
+
+## Strengths for this skill
+
+- **Configurable crawler** — backend choice (aiohttp, Scrapy), stealth mode, resume support.
+- **Distributed crawl** scales to 50K+ URL audits.
+- **`check_index`** uses Google PSE to spot-check indexed-or-not per URL.
+- Crawl output drops into MySQL workspace — easy to diff against log-derived URL sets.
+
+## How OurSEO pairs with log analysis
+
+1. **Logs** (`scripts/log_parser.py`) → what bots actually crawled at the origin
+2. **OurSEO crawl** → what URLs exist on the site today
+3. **Sitemap** → what URLs the site claims to publish
+4. **GSC** → what Google considers indexed
+5. **Diff all four** — orphan, ghost, and waste candidates emerge from set differences
+
+## Not for this skill when
+
+- **Actual bot User-Agent + frequency** — only logs show this.
+- **Per-bot status distribution** — only logs.
+- **First-party Googlebot crawl stats** — GSC.