feat: add package pruning system with configurable grace periods

- Implemented automatic pruning of stale packages across all platform sync endpoints (Arch, AUR, Debian, Ubuntu, Fedora, Homebrew, Winget)
- Added `last_seen_at` tracking to mark packages as seen during sync runs and identify inactive packages
- Introduced `PRUNE_GRACE_DAYS` and `PRUNE_HARD_DELETE_DAYS` environment variables for configurable soft-delete and hard-delete thresholds

src/services/packageService.ts

@@ -210,8 +210,8 @@ export class PackageService {
       `INSERT INTO packages (
         id, name, description, version, platform_id, category_id, 
         license_id, type, repository, homepage_url, download_url, 
-        popularity_score
-      ) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12) 
+        popularity_score, last_seen_at
+      ) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, NOW()) 
       RETURNING *`,
       [id, name, description, version, platform_id, category_id, 
        license_id, type, repository, homepage_url, download_url, 
@@ -238,6 +238,11 @@ export class PackageService {
       }
     }
 
+    // Always mark as seen and active on update
+    fields.push('last_seen_at = NOW()')
+    fields.push('is_active = true')
+    fields.push('updated_at = NOW()')
+
     if (fields.length === 0) {
       return this.getById(id)
     }