Fix L26: consolidate drag-drop URL extraction into shared urlHelpers

firstUrl() in DownloadBar was a local duplicate of looksLikeUrl iteration
(scanning multi-line text for the first valid URL). Promoted to
firstUrlInText() in src/renderer/src/lib/urlHelpers.ts alongside the other
URL utilities, re-exported from useClipboardLink.ts. DownloadBar now imports
firstUrlInText from there instead of maintaining a local copy.

typecheck + 242 tests green.

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

src/renderer/src/useClipboardLink.ts

@@ -3,7 +3,7 @@ import { useSettings } from './store/settings'
 // Pure URL helpers extracted to a standalone module so they can be tested
 // without pulling in the Zustand store (L40). Re-exported here for existing
 // consumers (DownloadBar, LibraryView) without an import-path change.
-export { looksLikeUrl, looksLikeSingleVideo } from './lib/urlHelpers'
+export { looksLikeUrl, looksLikeSingleVideo, firstUrlInText } from './lib/urlHelpers'
 import { looksLikeUrl } from './lib/urlHelpers'
 
 /** Where an offered link came from — drives the banner's wording. */