fix(snapshots): Address review bot findings for diff command

Use platform-specific binary name for odiff cache path so Windows gets
the required .exe extension. Always output diff masks with .png
extension regardless of input format. Include added/removed counts in
--fail-on-diff exit condition.

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

Author: NicoHinderling

src/commands/snapshots/diff.rs

@@ -200,7 +200,7 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
                 Ok(false) => {}
             }
 
-            let mask_path = output_dir.join(rel_path);
+            let mask_path = output_dir.join(rel_path).with_extension("png");
             if let Some(parent) = mask_path.parent() {
                 fs::create_dir_all(parent)?;
             }
@@ -331,14 +331,28 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
         "\nSummary: {total} total, {changed_count} changed, {unchanged_count} unchanged, {added_count} added, {removed_count} removed, {errored_count} errored",
     );
 
-    if fail_on_diff && (changed_count > 0 || errored_count > 0) {
+    if fail_on_diff
+        && (changed_count > 0 || errored_count > 0 || added_count > 0 || removed_count > 0)
+    {
         let mut parts = Vec::new();
         if changed_count > 0 {
             parts.push(format!(
                 "{changed_count} image{} differed from baseline",
                 if changed_count == 1 { "" } else { "s" }
             ));
         }
+        if added_count > 0 {
+            parts.push(format!(
+                "{added_count} image{} added",
+                if added_count == 1 { " was" } else { "s were" }
+            ));
+        }
+        if removed_count > 0 {
+            parts.push(format!(
+                "{removed_count} image{} removed",
+                if removed_count == 1 { " was" } else { "s were" }
+            ));
+        }
         if errored_count > 0 {
             parts.push(format!(
                 "{errored_count} image{} errored during comparison",

src/utils/odiff/binary.rs

@@ -28,7 +28,7 @@ fn cache_dir() -> Result<PathBuf> {
 fn download_and_extract() -> Result<PathBuf> {
     let binary_name = platform_binary_name()?;
     let cache = cache_dir()?;
-    let binary_path = cache.join("odiff");
+    let binary_path = cache.join(binary_name);
 
     fs::create_dir_all(&cache).context("Failed to create odiff cache directory")?;
 
@@ -99,8 +99,9 @@ pub fn ensure_binary() -> Result<PathBuf> {
         return Ok(system_path);
     }
 
+    let binary_name = platform_binary_name()?;
     let cache = cache_dir()?;
-    let cached_binary = cache.join("odiff");
+    let cached_binary = cache.join(binary_name);
     if cached_binary.exists() {
         info!("Using cached odiff at {}", cached_binary.display());
         return Ok(cached_binary);