feat(templates): add "Build it on Replit" button and replit-prompt section

[raoufchebri]

Summary

Adds a Build it on Replit action to DevHub templates and ships Replit-Agent prompts for the launch set of examples, cookbooks, and recipes.

When a template has a replit-prompt.md, the template usage banner renders a second action that opens replit.com with the prompt preloaded as an lz-string-compressed query param plus DevHub UTM tags. Templates without a replit-prompt.md are unchanged.

Plumbing

• Examples (already wired in c191572): content/examples/<slug>/replit-prompt.md is read by content-markdown.ts and forwarded to TemplateUsageBanner from example-detail.tsx.
• Cookbooks (new in 7de8fa3): added readCookbookReplitPrompt(), exposed replitPromptsBySlug from the cookbooks plugin, added a useCookbookReplitPrompt() hook, and threaded replitPrompt through useCookbookMarkdown → CookbookDetail → TemplateUsageBanner. validate-content.mjs now allows replit-prompt.md inside cookbook folders.
• Recipes (new in 7de8fa3): the file plumbing already supported replit-prompt.md; added useRecipeSections() and forwarded sections.replitPrompt from recipe-detail.tsx to the banner.

Replit prompts added

Tier	Slug
Example	saas-tracker (updated to add Genie analytics)
Example	vacation-rentals
Example	inventory-intelligence
Example	content-moderator
Cookbook	genie-analytics-app
Cookbook	operational-data-analytics
Recipe	genie-conversational-analytics
Recipe	genie-multi-space
Recipe	medallion-architecture-from-cdc
Recipe	volume-file-upload (Volume File Manager)

Each prompt follows the same structure: connector-first / PAT fallback decision tree, table or schema setup, app requirements, permission handling, build order, and scope notes.

Test plan

• npm run fmt
• npm run validate:content
• npm run typecheck
• npm run build
• npm run dev — server compiles cleanly, all 10 template routes load
• Manually click Build it on Replit on one example, one cookbook, and one recipe page and confirm the URL decompresses to the expected prompt
• Verify pages without a replit-prompt.md still render only the Copy prompt action