fix: send WhatsApp audio via native bridge media path

[EvolvingSoftwareAgent]

Summary

• add WhatsAppAdapter.send_voice()
• route WhatsApp audio through the existing bridge /send-media path
• add a regression test covering audio routing

Problem

WhatsApp outbound audio attachments were falling back to the base adapter's text behavior because gateway/run.py already routes audio media to adapter.send_voice(), but WhatsAppAdapter did not implement send_voice().

Test Plan

• local end-to-end manual test in WhatsApp chat confirmed audio attachment delivery after the fix
• pytest -q tests/gateway/test_whatsapp_connect.py -k send_voice_routes_to_bridge_audio_media
• full gateway test suite

[teknium1]

Thanks for the fix! The same send_voice() override already landed on main in commit ed76185 ("feat(whatsapp): implement send_voice for audio message delivery") via #12656, so this PR is now a no-op diff against current main. Closing as superseded — the behavior you fixed is in main today.

ed76185

[alt-glitch]

Likely duplicate of #13002 — same send_voice() override for WhatsApp adapter already merged.

[alt-glitch]

Likely duplicate of #13002