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

packages/npm-client/src/index.ts

@@ -5,44 +5,40 @@
 
 // Changes feed
 export {
-  fetchChanges,
   type Change,
   type ChangesFeedResponse,
   type FetchChangesOptions,
   type FetchChangesResult,
+  fetchChanges,
 } from './changes';
-
-// Keyword search
-export {
-  searchByKeyword,
-  searchAllByKeyword,
-  type SearchPackage,
-  type SearchResult,
-  type SearchResponse,
-  type SearchByKeywordOptions,
-} from './search';
-
-// Package metadata
-export {
-  fetchPackageMetadata,
-  fetchLatestPackageVersion,
-  fetchLatestPackageWithMetadata,
-  fetchPackageTpmjsField,
-  type PackageVersion,
-  type PackageMetadata,
-  type PackageVersionWithReadme,
-} from './package';
-
-// Download statistics
-export { fetchDownloadStats, fetchBulkDownloadStats, type DownloadsResponse } from './stats';
-
 // GitHub statistics
 export {
   fetchGitHubStars,
   fetchGitHubStarsFromRepository,
-  parseGitHubUrl,
   type GitHubRepoResponse,
+  parseGitHubUrl,
 } from './github';
 
+// Package metadata
+export {
+  fetchLatestPackageVersion,
+  fetchLatestPackageWithMetadata,
+  fetchPackageMetadata,
+  fetchPackageTpmjsField,
+  type PackageMetadata,
+  type PackageVersion,
+  type PackageVersionWithReadme,
+} from './package';
 // Rate limiting
-export { delay, RateLimiter, npmRateLimiter, retryWithBackoff } from './rate-limiter';
+export { delay, npmRateLimiter, RateLimiter, retryWithBackoff } from './rate-limiter';
+// Keyword search
+export {
+  type SearchByKeywordOptions,
+  type SearchPackage,
+  type SearchResponse,
+  type SearchResult,
+  searchAllByKeyword,
+  searchByKeyword,
+} from './search';
+// Download statistics
+export { type DownloadsResponse, fetchBulkDownloadStats, fetchDownloadStats } from './stats';