ui(thumbnail): size at 16:9 halfblock aspect and center vertically

The previous 20x10 image area was 1:1 in effective halfblock pixels,
so 16:9 source thumbnails fit-rendered as a 5-row strip glued to the
top-left corner — "stuck-on" rather than composed.

Resize to 32 cols x 9 rows = 32x18 halfblock pixels = 16:9 exact, so
typical YouTube/SoundCloud thumbnails fill the rectangle without
letterboxing. Wrap in a 34-col outer gutter with 1-char horizontal
margins, vertically centered between Min(0) spacers above and below.
Negative space becomes part of the composition — the image reads as
a deliberate anchor rather than an artifact.

No border/frame: matches looper's existing chrome-light aesthetic
(scatter visualizer is also unframed).

Author: program247365

src/tui.rs

@@ -337,15 +337,35 @@ fn draw_normal_in(frame: &mut ratatui::Frame, area: ratatui::layout::Rect, state
 
     draw_header(frame, chunks[0], state);
 
-    // If a thumbnail is loaded, give the left 20 columns to the image and
-    // let the visualizer flex into the remaining space; otherwise the
-    // visualizer fills the whole row as before.
+    // If a thumbnail is loaded, dedicate a 34-column gutter on the left to
+    // it and let the visualizer flex into the remaining space. The image
+    // itself is 32x9 char cells (16:9 in halfblock pixels — exact aspect
+    // match for typical YouTube/SoundCloud thumbnails), vertically centered
+    // in the gutter with 1-char horizontal margins. Negative space above
+    // and below is intentional: it makes the image read as an anchor rather
+    // than a corner sticker.
     let (image_area, scatter_area) = if state.thumbnail.is_some() {
-        let split = Layout::default()
+        let outer = Layout::default()
             .direction(Direction::Horizontal)
-            .constraints([Constraint::Length(20), Constraint::Min(20)])
+            .constraints([Constraint::Length(34), Constraint::Min(20)])
             .split(chunks[1]);
-        (Some(split[0]), split[1])
+        let vertical = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints([
+                Constraint::Min(0),
+                Constraint::Length(9),
+                Constraint::Min(0),
+            ])
+            .split(outer[0]);
+        let horizontal = Layout::default()
+            .direction(Direction::Horizontal)
+            .constraints([
+                Constraint::Length(1),
+                Constraint::Length(32),
+                Constraint::Length(1),
+            ])
+            .split(vertical[1]);
+        (Some(horizontal[1]), outer[1])
     } else {
         (None, chunks[1])
     };