Implement user soft-delete and improve search ranking

Adds soft-delete support for local users, including backend, API, and UI changes to allow admins to delete local users while preserving their requests. Updates user queries to exclude deleted users and allows username reuse for deleted accounts. Refines search and ranking logic for torrents: uses title-only queries for broader results, increases max results to 100, applies a minimum score threshold (30/100), and logs detailed ranking breakdowns. Updates the ranking algorithm to prioritize title/author match, adjusts scoring weights, and improves BookDate compatibility with Audiobookshelf by disabling rating-based features when unsupported. Enhances file copy operations for large files, improves metadata tagging, and updates documentation to reflect new search and ranking strategies.

prisma/schema.prisma

@@ -49,6 +49,10 @@ model User {
   bookDateCustomPrompt       String? @map("bookdate_custom_prompt") @db.Text
   bookDateOnboardingComplete Boolean @default(false) @map("bookdate_onboarding_complete")
 
+  // Soft delete support
+  deletedAt DateTime? @map("deleted_at")
+  deletedBy String?   @map("deleted_by") // Admin user ID who deleted this user
+
   // Relations
   requests                Request[]
   bookDateRecommendations BookDateRecommendation[]
@@ -56,6 +60,7 @@ model User {
 
   @@index([plexId])
   @@index([role])
+  @@index([deletedAt])
   @@map("users")
 }