feat: add notification sound volume slider (#2391)

* feat: add notification sound volume slider

Custom audio files vary widely in loudness; the new 0-100% slider in
Settings → Notifications lets the user lower an over-amplified sound
without re-encoding the file.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix: harden notification sound volume setting

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: Neil <4138956+nwparker@users.noreply.github.com>

src/shared/constants.ts

@@ -117,7 +117,8 @@ export function getDefaultNotificationSettings(): NotificationSettings {
     agentTaskComplete: true,
     terminalBell: false,
     suppressWhenFocused: true,
-    customSoundPath: null
+    customSoundPath: null,
+    customSoundVolume: 100
   }
 }
 

src/shared/types.ts

@@ -1339,6 +1339,7 @@ export type NotificationSettings = {
   terminalBell: boolean
   suppressWhenFocused: boolean
   customSoundPath: string | null
+  customSoundVolume: number
 }
 
 export type CodexManagedAccount = {