fix(live): index category lookups for catalog search (#49)

Avoid repeated category scans while filtering the paginated Live catalog, and keep the search timing and query-plan reproductions in the regression suite.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/db/sqlite.js

@@ -42,6 +42,8 @@ function initSchema() {
             data JSON -- Extra provider data
         );
         CREATE INDEX IF NOT EXISTS idx_categories_source_type ON categories(source_id, type);
+        CREATE INDEX IF NOT EXISTS idx_categories_source_type_category
+            ON categories(source_id, type, category_id);
     `);
 
     // Playlist Items (Channels, Movies, Series, Episodes)