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>

CODE-AUDIT.md

@@ -429,7 +429,7 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
 - [x] **L25 — Taskbar effect over-fires.** `App.tsx` subscribes to the whole downloads store and
   recomputes `summarizeQueue` + sends the taskbar IPC on *every* store change (each progress
   tick); throttle or dedupe by computed value.
-- [ ] **L26 — Third URL-sniffing path.** DownloadBar's drag-drop `firstUrl` is a separate
+- [x] **L26 — Third URL-sniffing path.** DownloadBar's drag-drop `firstUrl` is a separate
   "first http(s) line" extractor alongside `useClipboardLink.looksLikeUrl` and deeplink's scan.
 - [x] **L27 — DownloadBar Enter probes, not downloads.** Enter in the URL field triggers
   `fetchFormats`; there's no keyboard path to actually start the download (LibraryView's Enter