feat(calls): configurable ringtone volume in Settings (Bug #4 partial)

Adds 'Ringtone Volume' slider (0–100, default 70%) to Settings → Calls.
The IncomingCall audio element reads the setting and applies it as
audioElement.volume before playing, replacing the implicit browser
default of 1.0.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

LOTUS_BUGS.md

@@ -35,10 +35,11 @@ This document tracks identified bugs, edge cases, and architectural discrepancie
 ### 4. DM and Group Message Calls
 
 - **File:** `cinny/src/app/components/CallEmbedProvider.tsx`
-- **Status:** **OPEN**
+- **Status:** **PARTIALLY FIXED ⚠️ UNTESTED** — Volume control added. Remaining: ringtone selection, suppression during active calls.
 - **Issue:** Incoming call ringtone is hardcoded, lacks volume control, and is suppressed if the user is already in an active call.
 - **Root Cause:** Ringing logic is tightly coupled to `RTCNotification` events in `CallEmbedProvider.tsx`, using a hardcoded audio file path. It lacks an abstraction for sound management or user-configurable settings for ringtones/volumes.
-- **Proposed Fix:** Migrate sound asset management to a dedicated audio service. Implement user-configurable settings for ringtone and notification volume. Update the `IncomingCallListener` to support ringing even during active calls (if appropriate) by enhancing event handling.
+- **Fix Applied:** Added `ringtoneVolume` setting (0–100, default 70). `IncomingCall` reads this setting and applies `audioElement.volume = ringtoneVolume / 100` before `play()`. Slider added to Settings → General → Calls section.
+- **Remaining:** (a) Ringtone selection (still hardcoded to `call.ogg`); (b) Suppression during active calls — not investigated.
 
 ### 5. Seasonal Themes and Chat Backgrounds Design