feat: add indexes on tags.name and metas.name for improved query performance

Co-authored-by: aider (openai/andrew.openrouter.qwen.qwen3-coder) <aider@aider.chat>

src/db.rs

@@ -32,6 +32,8 @@ lazy_static! {
                  FOREIGN KEY(id) REFERENCES items(id) ON DELETE CASCADE,
                  PRIMARY KEY(id, name));"
         ),
+        M::up("CREATE INDEX idx_tags_name ON tags(name)"),
+        M::up("CREATE INDEX idx_metas_name ON metas(name)"),
     ]);
 }