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/19-seo-keyword-strategy/desktop/tools/ourseo.md

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+# OurSEO Agent (CLI + MCP)
+
+The OurSEO Agent (`~/Project/our-seo-agent`) covers two distinct paths for this skill:
+
+1. **CLI** — `our keywords *` (Claude Code, via Bash). DataForSEO under the hood. Cheapest per call, batch-friendly, Korean-aware.
+2. **MCP** — `mcp__ourseo__*` (Claude Desktop). Lighter surface: crawl, audit, Knowledge Graph entity expansion.
+
+Pick the path that matches your current Claude environment.
+
+## CLI commands (Claude Code, primary for Korean market)
+
+```bash
+# Volume + difficulty + intent
+our keywords volume "<keyword>" --location 2410 --language ko
+our keywords difficulty "<kw1>" "<kw2>" --location 2410
+our keywords intent "<kw1>" "<kw2>" "<kw3>"
+
+# Expansion
+our keywords ideas "<seed>" --location 2410 --limit 50
+our keywords for-site <competitor.com> --location 2410 --limit 100
+
+# Naver (Korean engines)
+our research naver keywords volume "<keyword>"
+our research naver keywords ideas "<keyword>" --limit 30
+
+# Cross-engine compare (where supported)
+our research keywords compare "<keyword>" --engines naver
+```
+
+| Location code | Market |
+|---|---|
+| `2410` | Korea |
+| `2840` | United States |
+| `2392` | Japan |
+
+| Language code | Language |
+|---|---|
+| `ko` | Korean |
+| `en` | English |
+| `ja` | Japanese |
+
+Cache (avoid duplicate calls): `our research cache list --engine <name>` / `our research cache clear --older-than 30d`.
+
+## MCP tools (Claude Desktop)
+
+| Tool | Purpose for keyword work |
+|---|---|
+| `mcp__ourseo__search_knowledge_graph` | Resolve a brand / entity to Knowledge Graph IDs — useful as a *seeding* step for keyword expansion around the entity. |
+| `mcp__ourseo__crawl_website` | Crawl the target site and pull on-page keyword inventory (title/h1/meta) — ground truth for what the site already targets. |
+| `mcp__ourseo__audit_page` | Single-page SEO audit; not a keyword tool per se, but useful for validating that high-value keywords are actually present on the page. |
+| `mcp__ourseo__check_serp` | Check SERP position for a keyword/domain pair — bridge to position tracking. |
+| `mcp__ourseo__find_similar_pages` | Semantic similarity over a prior crawl — supports topic clustering. |
+
+The OurSEO MCP does **not** expose DataForSEO keyword volume directly. For volume + KD + ideas in Claude Desktop, use Semrush MCP (`mcp__semrush__*`) or DataForSEO MCP (`mcp__dfs-mcp__*`).
+
+## Configuration
+
+The CLI reads from `~/Project/our-seo-agent/config/config.yaml` and these env vars:
+
+| Variable | Purpose |
+|---|---|
+| `DATAFORSEO_USERNAME` / `DATAFORSEO_PASSWORD` | DataForSEO auth |
+| `NAVER_CLIENT_ID` / `NAVER_CLIENT_SECRET` | Naver Open API + Search Ad |
+| `GOOGLE_KG_API_KEY` | Knowledge Graph Search API |
+
+See the project `CLAUDE.md` for full env-var reference. Credentials live in 1Password — fetch with `op://Development/<item>/credential`.
+
+## When to choose OurSEO over Semrush / Ahrefs
+
+- Korean-market batch work (Naver + Google together).
+- Crawl-derived keyword inventory (what the site itself targets, not estimates).
+- Knowledge Graph entity seeding.
+- Cost-sensitive bulk volume lookups.
+- Cross-engine comparison (Naver + DataForSEO via `our research keywords compare`).