feat(workspace): add full-text search for daily memory files

Add backend search command that performs case-insensitive matching
across all daily memory files, supporting both date and content queries.
Frontend includes animated search bar (⌘F), debounced input, snippet
display with match count badge, and search state preservation across
edits.

src-tauri/src/lib.rs

@@ -1051,6 +1051,7 @@ pub fn run() {
             commands::read_daily_memory_file,
             commands::write_daily_memory_file,
             commands::delete_daily_memory_file,
+            commands::search_daily_memory_files,
         ]);
 
     let app = builder