chore: move examples to app-templates repo

[thisistonydang]

Summary

Companion to databricks/app-templates#217. Migrates the six full-stack showcase examples (agentic-support-console, content-moderator, inventory-intelligence, rag-chat, saas-tracker, vacation-rentals) out of devhub/examples/ and into databricks/app-templates as flat top-level entries.

What this PR changes inside DevHub:

• Metadata schema — renames Example.githubPath to Example.templateUrl (full GitHub URL), decoupling the registry from the devhub repo layout. All six createExample() entries in src/lib/recipes/recipes.ts are updated accordingly.
• URL builders — api/content-markdown.ts, src/components/examples/example-detail.tsx, and src/lib/examples/build-example-markdown.ts now consume templateUrl directly. The hardcoded databricks/devhub + /template suffix logic is gone.
• initCommand rewrites — five git clone --depth 1 https://github.com/databricks/app-templates.git\ncd app-templates/<slug> plus the rag-chat databricks apps init --template …/app-templates/tree/main/rag-chat ….
• Example content — six content/examples/<slug>/goal.md files have their template/README.md references updated to README.md. The build-prompt narrative ("Clone and follow template/README.md") becomes "Clone and follow README.md".
• Authoring docs — CONTRIBUTING.md, .agents/skills/author-recipes-and-cookbooks/SKILL.md, and its references/quality-checklist.md rewritten to describe the new flat layout in app-templates (no template/ subdir, full URL in templateUrl).
• Deletes — the six examples/<slug>/template/ trees, plus the obsolete .gitattributes linguist rule for examples/*/template/package-lock.json (the file is now empty so the file itself is removed).
• examples/README.md — rewritten as a small stub pointing at app-templates and noting that vacation-rentals/blog-post-snippets/ is the only remaining child (kept here because it's blog supporting material referenced by jamesbroadhead/appkit-blog-snippets, not a runnable template).
• Tests — tests/build-example-markdown.test.ts, tests/e2e/copy-markdown.spec.ts, and tests/markdown.test.ts fixtures and assertions updated to reflect the new URLs and copy.

DevHub URL slugs (Example.id / /templates/<slug>) are unchanged. External blog post and docs links continue to resolve.

Dependency / merge order

The new templateUrl/initCommand strings point at paths in databricks/app-templates. Merge databricks/app-templates#217 first. Merging this PR before that one would temporarily leave the DevHub site with broken "View source on GitHub" links and broken databricks apps init --template … commands until app-templates lands.

Test plan

• npm run typecheck — pass
• npm run test — 269 / 269 unit + 107 / 107 e2e pass
• npm run validate:content — pass
• npm run verify:images — pass (64 raster images)
• npm run build — pass
• npm run fmt — applied
• Reviewer to spot-check that a deployed DevHub site shows correct "View source on GitHub" links once app-templates#217 is merged.

---

Co-authored-by: Cursor