feat(core,fuse,gui): "On this day" strip above the photos timeline

Add a PhotosOnThisDay control request, served from the stored timeline:
photos whose local capture date matches today's in earlier years, one
row per group. The GUI shows a card per year ("3 years ago") with the
year's newest photo as its cover; clicking a card scrolls the timeline
to that day. The strip is revealed only at the top of the whole,
unfiltered timeline, so it gives the grid its room back once you
scroll or filter.

crates/pdfs-fuse/src/control.rs

@@ -461,6 +461,16 @@ fn handle_control_conn(core: &Core, username: &str, mountpoint: &Path, stream: U
             },
             Err(e) => CtlResponse::error(e),
         },
+        Ok(CtlRequest::PhotosOnThisDay { limit }) => {
+            match core.photos_on_this_day(clamp_limit(limit)) {
+                Ok(items) => CtlResponse::Photos {
+                    available: true,
+                    items,
+                    counts: None,
+                },
+                Err(e) => CtlResponse::error(e),
+            }
+        }
         Ok(CtlRequest::PhotoGroup { uid }) => match core.photo_group(&uid) {
             Ok(items) => CtlResponse::Photos {
                 available: true,