[Bug] Voice messages fail cross-platform (device-dependent codec: webm/opus vs iOS)

[ThePhantomPuppet]

Voice recording uses whatever container/codec MediaRecorder gives the recording
browser (the mimeType picker just takes the first supported one). That is
device-dependent:

• Chrome/Android → audio/webm; codecs=opus
• iOS Safari → audio/mp4 (AAC)

iOS Safari cannot decode webm/opus in , so a voice message recorded on
Android often will not play on iOS (and other cross-platform mismatches).

Wanted: make voice messages play regardless of sender/receiver platform.

Options to weigh (do this with the attachment/#9 work):

• Pick the most cross-playable RECORD format the sender supports (prefer
  audio/mp4;codecs=mp4a on Safari, audio/webm;codecs=opus on Chrome) AND add a
  robust playback path + a decode-via-WebAudio fallback for waveform so
  the receiver can at least play it.
• If that isn't enough: decode (WebAudio) and re-encode to a universal format on
  the sender. WAV is universally playable but ~10x the size (blows the cap); MP3
  needs a WASM encoder (bundle weight); Opus-in-ogg/caf has partial iOS 17+
  support. Investigate what iOS actually plays today.
• Keep it inside the existing bitrate/size budget (VOICE_BITS_PER_SECOND).

Note the chosen container in the file name/mime so the receiver picks the right
playback path.