Add request approval system and audiobook path template

Implements admin approval workflow for user requests with global and per-user auto-approve controls. Adds new request statuses ('awaiting_approval', 'denied'), related API endpoints, and UI for pending approvals. Introduces configurable audiobook organization path template with validation and preview in settings, updates database schema and migrations for new fields.

prisma/migrations/20260115000000_add_audiobook_path_template/migration.sql

@@ -0,0 +1,17 @@
+-- Add audiobook path template configuration
+-- This allows admin to customize the folder/file path template for organized audiobooks
+-- Template supports placeholders: {author}, {title}, {asin}
+
+-- Insert default configuration for audiobook path template
+INSERT INTO configuration (id, key, value, encrypted, category, description, created_at, updated_at)
+VALUES (
+  gen_random_uuid(),
+  'audiobook_path_template',
+  '{author}/{title} {asin}',
+  false,
+  'automation',
+  'Template for organizing audiobook file paths. Supports placeholders: {author}, {title}, {asin}. Example: "{author}/{title} {asin}" creates "Author Name/Book Title ASIN/audiobook.m4b"',
+  NOW(),
+  NOW()
+)
+ON CONFLICT (key) DO NOTHING;