feat(image-picker): animated-image badge on GIF/WebP thumbnails

Animated thumbnails now show a small play-arrow badge (bottom-right) so users can
spot which images move before hovering; it's hidden while the image plays on
hover.

Detection is cheap — a new util::IsAnimatedImageFile probes without a full
decode: animated WebP via WebPGetFeatures.has_animation, and a multi-frame GIF
via a lightweight image-descriptor block walk (stops at the 2nd frame). The
picker only probes .gif/.webp thumbnails and caches the result on the Thumb.

Verified: animated GIF + animated WebP report animated; still GIF/WebP/PNG do not.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/util/texture_loader.h

@@ -31,6 +31,12 @@ struct AnimFrames {
  */
 bool LoadAnimatedRGBA(const char* path, int maxFrames, AnimFrames& out);
 
+/**
+ * @brief Cheaply report whether an image file is an animation (multi-frame GIF or animated WebP),
+ *        WITHOUT a full decode — a header/structure probe. False for stills + non-animatable formats.
+ */
+bool IsAnimatedImageFile(const char* path);
+
 /**
  * @brief Load a PNG/JPG/BMP image from disk into an OpenGL or DX11 texture.
  * @param path  File path (relative to working directory or absolute)