feat(app): polish pass - toasts, shortcuts, redesigned pages, cheaper frames

- toasts replace the status line; keyboard shortcuts with a ? overlay
- library: filters, sort, row virtualisation, cached search, skeleton
  tiles until the catalog loads, gradient placeholder art
- title page: season pills, episode rows with stills and one download
  glyph, portrait poster, clamped overview, resume time in the button
- player: fading chrome, smooth scrims, subtitles lifted over the
  controls, drag-following seek knob, OSD, speed menu, auto-skip
- settings as grouped cards with toggles and palette previews
- shares: confirm before removing, inline link validation, form kept
  until the add succeeds; downloads scroll and show rate and ETA
- downloads pipeline four blocks; the next episode is warmed near the end
- a film behind another page repaints at 4 Hz, not its frame rate

Fixes B55-B60.

crates/pstr-app/examples/embedded_video.rs

@@ -92,7 +92,12 @@ impl Harness {
             .context("eframe was built without a glow context")?;
         // SAFETY: `CreationContext` is handed to us on the UI thread with the
         // context current, which is the same guarantee `App::ui` gives.
-        let video = unsafe { VideoSurface::new(Arc::clone(&player), gl, cc.egui_ctx.clone()) }?;
+        let video = unsafe {
+            VideoSurface::new(Arc::clone(&player), gl, {
+                let ctx = cc.egui_ctx.clone();
+                move || ctx.request_repaint()
+            })
+        }?;
 
         Ok(Self {
             player,