fix(calls): hotkey rebind denylist; ignore modifiers; keep Space on buttons

- useKeyBind refuses Tab/Enter/arrows/Home/End/Page*/Escape and bare
  modifier codes, and refuses a code equal to the other call key, with an
  inline message (isBindableCallKey, unit-tested).
- PTT and deafen handlers ignore events with Ctrl/Alt/Meta held (deafen
  also Shift), so Cmd+M / Ctrl+M no longer toggle deafen.
- PTT only preventDefault()s when the target is not an interactive
  control, so Space still activates focused buttons during a call.

Fixes #23

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/settings/general/General.tsx

@@ -117,6 +117,7 @@ import { playCallJoinSound } from '../../../utils/callSounds';
 import { previewRingtone, RINGTONE_OPTIONS } from '../../../utils/ringtones';
 import { DenoiseTester } from './DenoiseTester';
 import { SettingsSelect } from '../../../components/settings-select/SettingsSelect';
+import { isBindableCallKey } from '../../../utils/callKeybind';
 
 /**
  * P5-47 — opt-in TDS window chrome toggle (desktop only). Renders nothing in the
@@ -1474,8 +1475,12 @@ function Privacy() {
   );
 }
 
-function useKeyBind(setter: (code: string) => void) {
+// [Gitea #23] Denylist navigation-critical/modifier codes and reject a code that
+// collides with the other call key (`otherKey`), so a rebind can never trap
+// keyboard focus in-call or silently double-bind PTT and deafen to the same key.
+function useKeyBind(setter: (code: string) => void, otherKey?: string) {
   const [listening, setListening] = useState(false);
+  const [error, setError] = useState<string | null>(null);
   const listenerRef = useRef<((e: KeyboardEvent) => void) | null>(null);
 
   useEffect(
@@ -1487,19 +1492,28 @@ function useKeyBind(setter: (code: string) => void) {
 
   const startListening = useCallback(() => {
     if (listening) return;
+    setError(null);
     setListening(true);
     const onKey = (e: KeyboardEvent) => {
       e.preventDefault();
-      if (e.code !== 'Escape') setter(e.code);
+      if (e.code === 'Escape') {
+        // Escape always cancels the rebind without changing the key.
+      } else if (!isBindableCallKey(e.code)) {
+        setError('That key can’t be bound — it’s needed for keyboard navigation.');
+      } else if (otherKey && e.code === otherKey) {
+        setError('That key is already bound to the other call shortcut.');
+      } else {
+        setter(e.code);
+      }
       setListening(false);
       window.removeEventListener('keydown', onKey, true);
       listenerRef.current = null;
     };
     listenerRef.current = onKey;
     window.addEventListener('keydown', onKey, true);
-  }, [listening, setter]);
+  }, [listening, setter, otherKey]);
 
-  return { listening, startListening };
+  return { listening, startListening, error };
 }
 
 const keyLabel = (code: string) =>
@@ -1556,8 +1570,8 @@ function Calls() {
     previewRingtone(value, Math.max(0, Math.min(1, ringtoneVolume / 100)));
   };
 
-  const pttBind = useKeyBind(setPttKey);
-  const deafenBind = useKeyBind(setDeafenKey);
+  const pttBind = useKeyBind(setPttKey, deafenKey);
+  const deafenBind = useKeyBind(setDeafenKey, pttKey);
 
   const mlSupported = isMLDenoiseSupported();
   const selectedDenoiseModel = DENOISE_MODELS.find((m) => m.id === callDenoiseModel);
@@ -1823,7 +1837,7 @@ function Calls() {
         {pttMode && (
           <SettingTile
             title="PTT Key"
-            description="Press a key to bind it as your push-to-talk key."
+            description={pttBind.error ?? 'Press a key to bind it as your push-to-talk key.'}
             after={
               <Button
                 size="300"
@@ -1841,7 +1855,9 @@ function Calls() {
         )}
         <SettingTile
           title="Push to Deafen"
-          description="Toggle speaker mute during a call. Press Escape to cancel rebind."
+          description={
+            deafenBind.error ?? 'Toggle speaker mute during a call. Press Escape to cancel rebind.'
+          }
           after={
             <Button
               size="300"