Refactor indexer management and improve search logic

Refactors admin settings to use a new IndexersTab and card-based indexer management UI, supporting category selection and improved configuration. Updates backend and API routes to handle indexer categories, propagate ASIN for better search scoring, and group indexers by categories to optimize Prowlarr searches. Enhances documentation to clarify non-terminal request matching and auto-completion behavior. Adds new reusable components for indexer management and category selection.

documentation/integrations/plex.md

@@ -80,6 +80,40 @@ API Docs: `/PlexMediaServerAPIDocs.json`
 **Benefits:** Lightweight polling for new items + comprehensive matching for downloaded requests
 **Note:** Requests transition: pending → searching → downloading → processing → downloaded → available (after detection)
 
+## Auto-Completion of Stuck Requests
+
+Library scans (full and incremental) now check **all non-terminal requests** for matches:
+
+**Eligible statuses:**
+- pending, searching, downloading, processing, downloaded
+- failed, awaiting_search, awaiting_import, warn
+
+**Excluded statuses:**
+- available (already completed)
+- cancelled (user cancelled)
+
+**Use Case:**
+1. Request stuck in 'awaiting_search' or 'failed' status
+2. User manually imports audiobook to library (via Plex/ABS or external tool)
+3. Next library scan (manual trigger or scheduled recently-added check)
+4. Request auto-matches and marks as 'available'
+5. Error messages and retry counters cleared
+
+**State Cleanup on Match:**
+- errorMessage → null
+- searchAttempts → 0
+- downloadAttempts → 0
+- importAttempts → 0
+- completedAt → scan timestamp
+
+**Edge Cases:**
+- Active downloads/jobs continue but become no-ops (download completes, organize skips)
+- Torrent/NZB remains in download client (manual cleanup if desired)
+
+**Logging:**
+- Transitions from non-downloaded statuses logged with original status: `Match found! "Book" → "Library Book" (was 'failed')`
+- Provides visibility into which stuck requests were auto-completed
+
 ## Data Models
 
 ```typescript