chore(seo-schema-generator): restore dual-platform code/ + desktop/ structure

The full-merge commit removed 17's code/ and desktop/ folders along with the old
template-fill generator, leaving 17 structurally inconsistent with 16 (and the repo's
documented dual-platform convention). Restore them for the MERGED skill:

- code/CLAUDE.md — Claude Code directive pointing to the root two-mode pipeline
  (no script duplication; root scripts/ stays the single source of truth).
- desktop/SKILL.md + skill.yaml — Claude Desktop directive for the two-mode skill.
- desktop/tools/{firecrawl,perplexity}.md — restored verbatim from git (still used by
  Mode 1 crawl / Mode 2 research).

The old generator's logic stays retired; only the dual-platform folder structure and
relevant tool docs return. 17 now matches 16's layout.

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

custom-skills/17-seo-schema-generator/desktop/skill.yaml

@@ -0,0 +1,14 @@
+# Skill metadata (extracted from SKILL.md frontmatter)
+
+name: seo-schema-generator
+description: |
+  JSON-LD generator with two modes — from an existing website, or from collected
+  sources for a not-yet-published site — both via a claims register. Triggers:
+  generate schema, create JSON-LD, source-to-schema, schema from site, claims register.
+
+# Optional fields
+allowed-tools:
+  - mcp__firecrawl__*
+  - mcp__perplexity__*
+
+# triggers: []  # TODO: Extract from description