Connect ConversationTab UI to Working AudioService

[FJiangArthur]

Priority: High
Phase: 1
Estimate: 2 story points

Description:
The ConversationTab UI is not properly connected to the AudioService. The record button, timer display, and waveform need to be integrated with the working audio service implementation.

Current Issues:

• Record button doesn't start actual recording
• UI doesn't reflect real recording state
• Timer and waveform show placeholder data

Acceptance Criteria:

• Record button starts/stops actual audio recording
• Timer displays real recording duration from AudioService
• Waveform shows actual audio levels from AudioService
• UI reflects current recording state (idle, recording, processing)
• Error states are properly displayed to user

Implementation Location:
lib/ui/widgets/conversation_tab.dart