[BUG] iOS dictation: text remains in Dispatch composer after send, requires manual clear

Describe the bug

When using iOS native dictation (the workaround for the missing mic icon, see related issue), tapping send dispatches the message correctly BUT does not clear the composer text field. User must manually triple-tap → select all → delete before dictating the next message.

Repro

1. Open Dispatch session on iPad
2. Tap iPad keyboard mic / hold space bar to dictate
3. Speak a message
4. Tap send arrow
5. Message goes through correctly
6. BUG: dictated text remains in the composer

Expected

After successful send, composer field should be empty, ready for next message — same as the keyboard input behavior.

Actual

Field still contains the previously-sent text. User has to:

1. Triple-tap text to select-all
2. Delete
3. Then dictate next message

This 3-step extra action between every message makes voice-only workflow painful.

Severity

HIGH for accessibility users who rely on voice input as primary mode.

Environment

• iPad / iPadOS
• Claude app — Dispatch mode
• Using iOS system dictation (not in-app mic since that's missing — see related issue)

Possible cause

Looks like the composer's clear-on-send handler doesn't fire when input came from the dictation accessory view, only from the keyboard onChange.