feat(ui): speaker glyph + searchable output-device select

QbzSelect badges now render a "BP" tag for bit-perfect outputs and a
speaker glyph (volume-2) for the rest (real outputs that play audio but
not bit-perfect) — an addition, not a replacement. Only the device select
passes badges, so other selects are unchanged.

Add opt-in `searchable`: long output lists overflowed at 1440p, so the
open list gets a case-insensitive filter box and a 360px scroll cap.
Filtering hides non-matching rows by visibility only (model order intact,
so selected(i) keeps the original index). Backed by a new Rust
TextUtil.contains-ci pure callback (Slint 1.16 has no contains builtin).

cc

crates/qbz-slint/src/main.rs

@@ -3712,6 +3712,17 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             });
     }
 
+    // Case-insensitive substring test backing the searchable QbzSelect
+    // (Slint 1.16 has no `contains` builtin). Pure + stateless, so a single
+    // registration at setup serves every searchable list.
+    window
+        .global::<TextUtil>()
+        .on_contains_ci(|haystack: slint::SharedString, needle: slint::SharedString| {
+            haystack
+                .to_lowercase()
+                .contains(needle.to_lowercase().as_str())
+        });
+
     // Genre filter — selection is per context ("discover" / "favorites").
     // Toggling / clearing re-fetches the discover index (discover context)
     // or re-derives the favorites tab (favorites context).