Clip counts on listings, so clients find photos with only clips

Derived clips (#208) aren't counted as versions, so a photo whose only
derived file is a clip looked like a plain photo, and clients never fetched
/image/versions for it. Summaries now carry clip_count: /photos adds the
parallel array photo_clip_counts, records (memories, search, /photos/exif)
carry clip_count. All skipped when zero, so other responses are unchanged.

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

src/data/mod.rs

@@ -125,6 +125,11 @@ pub struct PhotosResponse {
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub photo_version_counts: Vec<u32>,
 
+    /// How many derived clips (videos made from the photo, e.g. Animate)
+    /// stand behind `photos[i]`; skipped when the page has none.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub photo_clip_counts: Vec<u32>,
+
     // Pagination metadata (only present when limit is set)
     #[serde(skip_serializing_if = "Option::is_none")]
     pub total_count: Option<i64>,