Context

This PR works around a 1-2 second audio silence that occurs when unmuting for the first time during a call for Bluetooth headphone users with mute_on_join enabled. Bluetooth headphones must switch from A2DP (listening-only) to HFP (microphone-enabled) mode when the mic is first activated, which interrupts audio output. Now the microphone track opens on join (still muted at the publication level), moving this switch to when users already expect a connection delay / audio instability. It should be noted that I expect that the OS microphone indicator will now appear on channel join rather than on first unmute, but I feel this is a justified side effect:

1. This is consistent with other apps—joining a Slack huddle with "Mute my microphone" enabled also shows the indicator immediately on join while muted.
2. Zed users without mute_on_join already see the OS-level microphone indicator for the entire call (even after muting) and already experience the Bluetooth profile switch at join time—this change simply brings mute_on_join users in line with that existing behavior.

How to Review

Self-Review Checklist

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Fixed 1-2 seconds of audio silence when unmuting for the first time during a call with Bluetooth headphones when mute_on_join is enabled.