fix(images): pick the decoder from the bytes, not the extension

`image::open` chooses the decoder by extension, so a PNG saved as .jpg
(Android screenshots, chat exports) failed thumbnails, previews,
perceptual hashes, insights and face crops with "Illegal start bytes:
8950". New `file_types::open_image` sniffs the header and falls back to
the extension when it's unknown; every decode site uses it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/thumbnails.rs

@@ -104,7 +104,7 @@ pub fn generate_image_thumbnail(src: &Path, thumb_path: &Path) -> std::io::Resul
         return generate_image_thumbnail_ffmpeg(src, thumb_path, orientation);
     }
 
-    let img = image::open(src).map_err(|e| {
+    let img = file_types::open_image(src).map_err(|e| {
         std::io::Error::new(std::io::ErrorKind::InvalidData, format!("{:?}: {}", src, e))
     })?;
     let img = exif::apply_orientation(img, orientation);
@@ -148,7 +148,7 @@ pub fn generate_preview(src: &Path, dest: &Path, max_dim: u32) -> std::io::Resul
         return generate_preview_ffmpeg(src, dest, orientation, max_dim);
     }
 
-    let img = image::open(src).map_err(|e| {
+    let img = file_types::open_image(src).map_err(|e| {
         std::io::Error::new(std::io::ErrorKind::InvalidData, format!("{:?}: {}", src, e))
     })?;
     let img = exif::apply_orientation(img, orientation);