Add rootless Podman fixes, and others

improve container startup for rootless Podman, plus related refactors and tests. Key changes:

- Add/modify Audiobookshelf-related code and wiring (src/lib/services/audiobookshelf/api.ts, library service refs) and update documentation TABLEOFCONTENTS to reference ABS implementation.
- Detect user namespace in docker/unified app-start.sh and redis-start.sh and skip gosu when running in rootless Podman to preserve UID mapping; improve startup logging and verification.
- Add utility/service files (auth-token-cache.service.ts, credential-migration.service.ts, cleanup-helpers.ts) and corresponding tests; update chapter-merger and metadata-tagger utilities/tests.
- Update many admin/auth API routes and tests to reflect changes in settings and integrations.
- Remove large AI agent and Audiobookshelf implementation guide docs (AGENTS.md and the implementation guide) and add README note about AI-assisted workflow.

These changes enable Audiobookshelf backend mode, improve compatibility with rootless container runtimes, and include cleanup/refactor work and unit tests.

src/lib/integrations/qbittorrent.service.ts

@@ -1027,8 +1027,8 @@ export async function getQBittorrentService(): Promise<QBittorrentService> {
         pathMappingEnabled: clientConfig.remotePathMappingEnabled,
       });
 
-      // Validate required fields
-      if (!clientConfig.url || !clientConfig.username || !clientConfig.password) {
+      // Validate required fields (only URL is required - username/password optional for whitelist users)
+      if (!clientConfig.url) {
         throw new Error('qBittorrent is not fully configured. Please check your configuration in admin settings.');
       }
 
@@ -1045,8 +1045,8 @@ export async function getQBittorrentService(): Promise<QBittorrentService> {
       logger.info('[QBittorrent] Creating service instance...');
       qbittorrentService = new QBittorrentService(
         clientConfig.url,
-        clientConfig.username,
-        clientConfig.password,
+        clientConfig.username || '',
+        clientConfig.password || '',
         downloadDir,
         clientConfig.category || 'readmeabook',
         clientConfig.disableSSLVerify,