feat: add crop recovery and recompression survival

Adds dimension-search crop recovery that tries candidate original sizes
to reconstruct the embed grid, and fixes test imports for GenericImageView.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/idfoto-core/src/imgsecret.rs

@@ -555,6 +555,7 @@ fn extract_with_crop_recovery(jpeg_bytes: &[u8]) -> Result<[u8; 32]> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use image::GenericImageView;
 
     fn make_test_jpeg(width: u32, height: u32) -> Vec<u8> {
         use image::codecs::jpeg::JpegEncoder;