Docs reorg, config refactor, and ItemValues index fix

- Moved all documentation to docs/ and updated README with categorized links and new docs/INDEX.md
- Added HOW_TO_SWITCH_DATABASE.md and several new analysis/action docs
- Introduced db-config.ps1 for centralized DB config; all scripts now use it for easy DB switching
- Added db-quick.ps1 for interactive diagnostics and index management
- Updated Add-All-Indexes.bat to use db-config.ps1
- Added Fix-ItemValues-Performance.ps1 to create 3 critical indexes on ItemValues, addressing 1.3B row seq scan issue
- Updated performance_indexes.sql with new ItemValues indexes and ANALYZE
- Updated diagnostics.sql and database_report.txt for improved output and clarity
- All scripts and docs now reference the new config and index optimization workflow

Add-All-Indexes.bat

@@ -10,10 +10,14 @@ echo - 18 base performance indexes
 echo -  5 supplementary indexes
 echo Total: 23 indexes
 echo.
+echo NOTE: This uses the database configured in db-config.ps1
+echo Current default: jellyfin_testsdata
+echo.
 echo This may take 10-30 minutes...
 echo.
 
-"C:\Program Files\PostgreSQL\18\bin\psql.exe" -U jellyfin -d jellyfin -f sql\all_performance_indexes.sql
+REM Use PowerShell to load config and run
+powershell -Command ". .\db-config.ps1; & $PSQL_PATH -U $DB_USER -d $DB_NAME -f sql\all_performance_indexes.sql"
 
 if %ERRORLEVEL% EQU 0 (
     echo.