- Add library_ai_settings table with migration for per-library overrides - Extend AiConfig with editable prompt parts for description, tagging, extraction, and translation steps; defaults match previous hardcoded values - Add getEffectiveAiConfig(libraryId) that merges global settings with library-level overrides (empty override falls through to global) - Update all ai-tagger functions to use getEffectiveAiConfig and build prompts from configurable parts - Add GET/PUT /api/ai-settings/library/[id] for per-library overrides - Update /api/ai-settings GET/PUT to include prompt fields - Add Prompts section and Library Overrides section to admin UI Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>