docs: complete API keys documentation in README.md

Documentation Enhancement:
- Add missing TVDB_API_KEY to all relevant sections in README.md
- Create comprehensive API keys reference table with purposes and sources
- Add centralized API Keys Configuration section with clear examples
- Document how to resolve "TVDB API key not configured" warnings
- Include direct links to obtain API keys from each service

API Keys Covered:
- TMDB_API_KEY - Movie release dates and metadata fallbacks
- TVDB_API_KEY - TV show metadata and Emby compatibility (was missing!)
- RADARR_API_KEY - Movie import history and database access
- SONARR_API_KEY - TV episode import history

This resolves user questions about the TVDB API key warning and provides
complete documentation for all external API integrations.

SUMMARY.md

@@ -413,6 +413,24 @@ Curl scan → Check database → Find 8:30am webhook entry → NFO shows 8:30am
 
 ---
 
+---
+
+### 🆕 v0.7.2 Complete API Keys Documentation (September 2025)
+
+**📚 Enhanced README.md Documentation:**
+- **Missing TVDB_API_KEY**: Added TVDB API key to all relevant sections
+- **Comprehensive API Table**: Complete reference for all API keys with purposes and sources
+- **Configuration Examples**: Clear examples for .env.secrets setup  
+- **Warning Resolution**: Documentation for resolving "TVDB API key not configured" warnings
+- **Easy Reference**: Centralized API keys section with direct links to get keys
+
+**🔧 What This Fixes:**
+- **TVDB Warning**: Users can now easily resolve `[WARNING] TVDB API key not configured, skipping TVDB ID lookup`
+- **Complete Documentation**: All API keys (TMDB, TVDB, Radarr, Sonarr) properly documented
+- **User Experience**: Clear table showing which keys are required vs optional
+
+---
+
 **Last Updated:** September 14, 2025  
-**Version:** v0.7.1  
+**Version:** v0.7.2  
 **Status:** Production Ready - Major Architecture