fix(shell): macOS NPB-Small bottom clearance via Rust-set npb-small-extra

The 2px .slint literal proved invisible (owner ask 2026-07-21, iteration
2026-07-22). The extra clearance is now set from Rust at startup
(ShellState.npb-small-extra, default 6px, macOS-only, QBZ_NPB_SMALL_EXTRA
env override) so tuning costs a ~2-minute qbz-bin rebuild instead of a
~2 h qbz-ui one on the 8 GB Mac. Linux stays pixel-identical (extra = 0).

km

crates/qbz-ui/ui/shell/PlayerBarSmall.slint

@@ -126,9 +126,10 @@ export component PlayerBarSmall inherits Rectangle {
 
     // One bar, header-height tall: a 3px top seekbar strip + the controls row
     // that fills the rest (no band bump — the large album art defines the height).
-    // macOS: +2px (ShellState.npb-small-height) so the meta line never clips at
-    // the window's bottom edge; the song card below keeps its 39px top-anchored
-    // geometry, so the extra height lands as bottom clearance.
+    // macOS: taller by ShellState.npb-small-extra (Rust-set, default 6px) so
+    // the meta line never clips at the window's bottom edge/bezel; the song
+    // card below keeps its 39px top-anchored geometry, so the extra height
+    // lands as bottom clearance.
     height: ShellState.npb-small-height;
     background: ShellState.app-background-active
         ? Theme.surface-card.with-alpha(AppearanceState.app-background-surface-alpha)
@@ -229,11 +230,11 @@ export component PlayerBarSmall inherits Rectangle {
                     // The wrapper takes the row's vertical stretch; the card
                     // itself is pinned to the pre-2.0.2 39px top-anchored
                     // geometry (Layout.header-height − 3px seekbar) so macOS's
-                    // +2px bar (ShellState.npb-small-height) lands BELOW the
-                    // card: the art keeps its exact top-relative position and
-                    // the meta line gains 2px of bottom clearance (owner ask
-                    // 2026-07-21). Linux: wrapper height == card height →
-                    // pixel-identical to before.
+                    // taller bar (ShellState.npb-small-extra, Rust-set) lands
+                    // BELOW the card: the art keeps its exact top-relative
+                    // position and the meta line gains the extra as bottom
+                    // clearance (owner ask 2026-07-21). Linux: wrapper height
+                    // == card height → pixel-identical to before.
                     Rectangle {
                         horizontal-stretch: 1;
                         SongCard {

crates/qbz-ui/ui/state.slint

@@ -4031,14 +4031,20 @@ export global ShellState {
     // "new"|"classic"|"small"|"large"); set on startup from the store and on the
     // player bar's "Now Playing view" menu select.
     in-out property <int> npb-mode: 0;
-    // Small-mode (2) bar height. macOS-only +2px (owner ask 2026-07-21): the
+    // Small-mode (2) bar extra bottom clearance (owner ask 2026-07-21): the
     // compact bar's CJK/descender-heavy meta line clipped at the window's
-    // bottom edge. The bar is bottom-anchored, so it grows UPWARD;
-    // PlayerBarSmall pins the song card to its old top-anchored geometry so
-    // the art keeps its position and the 2px land as bottom clearance.
+    // bottom edge/bezel on macOS. The bar is bottom-anchored, so it grows
+    // UPWARD; PlayerBarSmall pins the song card to its old top-anchored
+    // geometry so the art keeps its position and the extra lands as bottom
+    // clearance. The AMOUNT is set from Rust at startup (main.rs, macOS-only
+    // — 0 elsewhere; QBZ_NPB_SMALL_EXTRA env override for tuning) because a
+    // .slint literal costs a ~2 h qbz-ui rebuild on the 8 GB Mac per
+    // iteration, a Rust-side constant ~2 min. 2px proved invisible
+    // (2026-07-22).
+    in-out property <length> npb-small-extra: 0px;
     // (42px == Layout.header-height; literal kept so state.slint needs no
     // foundation import — same precedent as large-dock-width below.)
-    out property <length> npb-small-height: 42px + (AppearanceState.is-macos ? 2px : 0px);
+    out property <length> npb-small-height: 42px + root.npb-small-extra;
     // Large NPB (mode 3) is only valid while the sidebar is OPEN (state 0): the
     // cover + spectrum dock lives at the bottom of the open sidebar. Views read
     // this to mount the dock and to drive the FFT visualizer tap.