Filter non-browser-playable formats from Doom Scroll

Formats like .mkv, .avi, .wmv, .ts, .m2ts and .tiff are not natively
supported by browsers and would stall silently in Doom Scroll mode.

Add src/lib/browser-media.ts with BROWSER_VIDEO_EXTENSIONS (.mp4,
.webm, .mov, .m4v), BROWSER_IMAGE_EXTENSIONS (.jpg, .jpeg, .png, .gif,
.webp, .bmp), and an isBrowserPlayable() helper that extracts the
extension without importing Node's path module.

Filter doomScrollItems in MixedView, MoviesView, and TvView using this
helper so only natively renderable files are passed to DoomScrollView.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/browser-media.ts

@@ -0,0 +1,19 @@
+/**
+ * Browser-native media formats safe for use in <video> and <img> elements.
+ * Kept separate from the broader scanner extension sets (media-utils.ts, files.ts)
+ * which include server-side-only formats like .mkv, .avi, .tiff, etc.
+ */
+
+export const BROWSER_VIDEO_EXTENSIONS = new Set(['.mp4', '.webm', '.mov', '.m4v'])
+export const BROWSER_IMAGE_EXTENSIONS = new Set(['.jpg', '.jpeg', '.png', '.gif', '.webp', '.bmp'])
+
+/**
+ * Returns true if the file at `filename` (or path) has a browser-playable extension.
+ * Uses lastIndexOf to avoid importing the Node `path` module in client components.
+ */
+export function isBrowserPlayable(filename: string): boolean {
+  const dot = filename.lastIndexOf('.')
+  if (dot === -1) return false
+  const ext = filename.slice(dot).toLowerCase()
+  return BROWSER_VIDEO_EXTENSIONS.has(ext) || BROWSER_IMAGE_EXTENSIONS.has(ext)
+}