fix: address codebase review issues

- refactor(backend): use tokio::sync::Mutex for DbState and update commands to async
- fix(backend): remove unconditional post-queue system action in scheduler
- refactor(backend): remove dead WebSocket aria2 progress loop
- fix(backend): use character count for deep link payload length check
- fix(backend): implement dynamic port fallback for extension server
- build(backend): apply macos codesigning step for release builds
- security(backend): add explicitly defined Content-Security-Policy
- fix(frontend): replace pause_download API call with remove_download for file cleanup
- fix(frontend): resolve bug ignoring 0% progress reporting
- fix(frontend): append instead of overwrite deep link URLs when Add Modal is open
- style(frontend): append standard .dark class for dark mode themes
- style(frontend): remove ghost row layout hack from download table
- build: decouple typescript binding generation from build step

src/components/DownloadTable.tsx

@@ -306,17 +306,7 @@ export const DownloadTable: React.FC<DownloadTableProps> = ({ filter }) => {
                   </div>
                 </div>
               ))}
-              <div className="flex-1 overflow-hidden flex flex-col pointer-events-none">
-                {Array.from({ length: 50 }).map((_, index) => {
-                  const isEven = (filteredDownloads.length + index) % 2 === 1;
-                  return (
-                    <div 
-                      key={`ghost-${index}`} 
-                      className={`download-ghost-row ${isEven ? 'striped' : ''}`} 
-                    />
-                  );
-                })}
-              </div>
+              <div className="flex-1 bg-transparent pointer-events-none"></div>
             </div>
             </div>
             </div>