feat: add use cases marketing product with AI-generated content

Transform qualifying scenarios into marketing-ready use cases with:
- AI-generated titles, descriptions, ROI estimates, business value
- Persona/industry/category taxonomy for targeting
- Browseable feed with filtering and ranking
- SEO-optimized case study pages
- Daily cron job for generation and ranking

Database:
- Add Persona, Industry, Category lookup tables
- Add UseCase model with marketing content fields
- Add junction tables for personas/industries/categories
- Add SocialProof model for cached metrics

API:
- GET /api/use-cases - Global directory with filtering
- GET /api/use-cases/[id] - Individual use case details
- GET /api/public/users/[username]/collections/[slug]/use-cases
- POST /api/cron/use-cases - Nightly generation job

Frontend:
- /use-cases - Global feed with persona dropdown
- /use-cases/[slug] - SEO case study page
- /[username]/collections/[slug]/use-cases - Collection feed
- UseCasesFeed component - Sortable table component
- UseCaseCaseStudy component - Full case study layout

apps/web/src/app/docs/executors/page.tsx

@@ -214,8 +214,7 @@ export default function ExecutorsDocsPage(): React.ReactElement {
             {/* GET /health */}
             <div className="mb-8">
               <h3 className="text-lg font-medium text-foreground mb-2">
-                <code className="px-2 py-1 bg-success/10 text-success rounded">GET</code>{' '}
-                /health
+                <code className="px-2 py-1 bg-success/10 text-success rounded">GET</code> /health
               </h3>
               <p className="text-foreground-secondary mb-4">
                 Check executor health status. Used by TPMJS to verify the executor is reachable.