feat(lotus): remember each person's volume across calls (#36)

The per-participant volume slider lived only in the tile's view model, so it
reset to 100 % on the next call, a reload, or when that person reconnected.

- lotus/lotusVolumeMemory.ts: per-Matrix-user volume in localStorage
  (`lotus-per-user-volume`), keyed by user id so it follows them across
  devices; 1 (100 %) forgets the entry; at most 50 people, least recently set
  dropped first; junk in storage ignored. Local only, never synced.
- VolumeControls take an optional initialVolume and onCommit; remote user
  media seeds from and saves to the memory. Screenshare audio stays per-share.
- commitPlaybackVolume now takes the slider's committed value. With the
  keyboard the slider commits before its last change arrives, so the
  committed (and remembered) volume was one step behind, and returning to
  100 % with End never registered.

Verified in a two-person local call: Alice sets Bob to 70 % with the
keyboard → audio element 0.70, stored 0.7; leave + rejoin → slider and audio
0.70; End → entry removed. Unit tests: memory module (LRU, reset, junk),
remembered volume restore + commit-with-value; state/tile/room/lotus suites
all pass on Node 22 (410 tests).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/tile/SpotlightTile.tsx

@@ -337,7 +337,10 @@ const ScreenShareVolumeButton: FC<ScreenShareVolumeButtonProps> = ({ vm }) => {
     (v: number) => vm.adjustPlaybackVolume(v),
     [vm],
   );
-  const onVolumeCommit = useCallback(() => vm.commitPlaybackVolume(), [vm]);
+  const onVolumeCommit = useCallback(
+    (value: number) => vm.commitPlaybackVolume(value),
+    [vm],
+  );
 
   return (
     audioEnabled && (