Fix M10: consolidate .url Internet Shortcut parsing into shared utility

Both DownloadBar (renderer, drag-drop) and deeplink.ts (main, argv) had their
own regex to extract URL= from a Windows Internet Shortcut file -- with subtly
different patterns (/^\s*URL\s*=\s*(\S+)/ vs /^URL=(.+)$/).

Added parseUrlShortcutContent() to @shared/ipc. Both callers now delegate to
it and apply their own http/https guard (looksLikeUrl in renderer, asHttpUrl
in main). The local parseUrlFile wrapper in DownloadBar is kept as the
validation compositing point; it's now a one-liner.

typecheck + 242 tests green.

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

src/renderer/src/components/DownloadBar.tsx

@@ -36,6 +36,7 @@ import { Select } from './Select'
 import { Hint } from './Hint'
 import { SegmentedControl } from './ui/SegmentedControl'
 import { IconButton } from './ui/IconButton'
+import { parseUrlShortcutContent } from '@shared/ipc'
 import { useClipboardLink, looksLikeUrl } from '../useClipboardLink'
 import { logError } from '../reportError'
 import { THUMB_LG } from '../thumbSizes'
@@ -52,8 +53,7 @@ function firstUrl(text: string): string | null {
 
 /** Pull the URL= target out of a dropped Windows .url Internet Shortcut file. */
 function parseUrlFile(content: string): string | null {
-  const m = /^\s*URL\s*=\s*(\S+)/im.exec(content)
-  const url = m?.[1]?.trim()
+  const url = parseUrlShortcutContent(content)
   return url && looksLikeUrl(url) ? url : null
 }