capture_loop: honour ENBOXER_ENABLE_TOPLEVEL via capture_toplevel (Bug #8)

Bug from Grok round-1 #8. capture_loop hard-coded grim and ignored the
toplevel-export gate. If the operator set ENBOXER_ENABLE_TOPLEVEL=1
they got no effect at all -- the loop just kept grimming the source
rect.

Fix: when the gate is set, build a synthetic Client (the hit has only
the source rect; pick_output_for queries live monitors to find one
covering the rect) and try capture_toplevel first. On success show
the frame; on failure fall through to grim so the operator at least
sees the visible background rather than an empty frame.

cargo test 96+/0; clippy clean.

src/vfx.rs

@@ -330,6 +330,30 @@ pub async fn capture_loop(rx: watch::Receiver<Vec<FeedHit>>, hub: Arc<OverlayHub
         for f in feeds {
             let dest = frame_path(&f.name);
             let (x, y, w, h) = f.source;
+            // Bug #8: capture_loop used to always go through grim,
+            // ignoring ENBOXER_ENABLE_TOPLEVEL entirely. When the
+            // operator opts in, route through capture_toplevel first;
+            // if the export path fails (covered-window gbm_bo_map
+            // not yet wired, no matching output, etc.) the grim
+            // fallback below still produces a frame.
+            if toplevel_enabled() {
+                let transient = crate::hypr::Client {
+                    address: format!("hit:{}", f.name),
+                    class: "enboxer-vfx".into(),
+                    title: f.name.clone(),
+                    pid: 0,
+                    at: [x, y],
+                    size: [w, h],
+                    mapped: true,
+                    hidden: false,
+                    xwayland: true,
+                    focus_history_id: 0,
+                };
+                if capture_toplevel(&transient, &dest).await.is_ok() {
+                    let _ = hub.show_frame(&f.name, &dest).await;
+                    continue;
+                }
+            }
             if capture_region(x, y, w, h, &dest).await.is_ok() {
                 let _ = hub.show_frame(&f.name, &dest).await;
             }