style: apply cargo fmt across the crate (A20)

The repo never enforced rustfmt, so formatting had drifted broadly. This is a
single mechanical `cargo fmt` pass over the whole crate (no behavioral change;
lib suite green, 493 passed). Going forward fmt should be enforced (planned CI
fmt --check step). Part of the 0.6.1 hygiene pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/hotkeys.rs

@@ -89,9 +89,9 @@ impl HotkeyAction {
 
     pub fn tier(self) -> HotkeyTier {
         match self {
-            HotkeyAction::ToggleMute
-            | HotkeyAction::ToggleDeafen
-            | HotkeyAction::OpenSettings => HotkeyTier::AppWide,
+            HotkeyAction::ToggleMute | HotkeyAction::ToggleDeafen | HotkeyAction::OpenSettings => {
+                HotkeyTier::AppWide
+            }
             HotkeyAction::PushToTalk | HotkeyAction::LeaveRoom => HotkeyTier::RoomOnly,
         }
     }
@@ -278,7 +278,10 @@ mod tests {
 
     #[test]
     fn parse_single_character_case_folds() {
-        assert_eq!(parse_binding("M"), Some(KeyBinding::Character("m".to_string())));
+        assert_eq!(
+            parse_binding("M"),
+            Some(KeyBinding::Character("m".to_string()))
+        );
         assert_eq!(format_binding(parse_binding("m").as_ref()), "M");
     }
 }