fix(calls): Push to Deafen can be switched off, and a typable deafen key can no longer fire while typing

Root cause of the 'went deaf while typing' reports: the deafen key (default
M) and Cinny's type-anywhere-to-focus-the-composer both listen on window,
so the first letter of a message typed after clicking the timeline toggled
deafen and was swallowed (reproduced: typing 'mom' → deafened, composer
shows 'om'). Now: (1) Settings → Calls → Push to Deafen has an on/off
switch (deafenHotkey); (2) a letter/digit/Space deafen key only toggles
where no composer is on screen — typing wins; (3) such keys are never
bound system-wide on desktop — only F-keys, numpad and the lock/navigation
cluster qualify (isSafeGlobalToggleKey) — so 'm' typed in another app
can't deafen you. Verified in live calls: M still toggles in the call
view, is ignored on a chat screen, switch off disables it entirely.

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

src/app/state/settings.ts

@@ -260,6 +260,8 @@ export interface Settings {
   glassmorphismSidebar: boolean;
 
   deafenKey: string;
+  /** Master switch for the push-to-deafen key (both in-window and system-wide). */
+  deafenHotkey: boolean;
 
   warnOnUnverifiedDevices: boolean;
 
@@ -381,6 +383,7 @@ const defaultSettings: Settings = {
   glassmorphismSidebar: false,
 
   deafenKey: 'KeyM',
+  deafenHotkey: true,
 
   warnOnUnverifiedDevices: false,