Fix Recording Timer to Show Actual Elapsed Time

[FJiangArthur]

Priority: High
Phase: 1
Estimate: 1 story point

Description:
The recording timer in the ConversationTab shows random numbers instead of actual elapsed recording time.

Current Issues:

• Timer displays random numbers like "03:47" when recording just started
• Timer doesn't increment consistently during recording
• Timer doesn't reset properly when recording stops

Acceptance Criteria:

• Timer starts at 00:00 when recording begins
• Timer increments every second during active recording
• Timer stops when recording ends
• Timer resets to 00:00 for new recordings
• Timer format is MM:SS consistently

Implementation Location:
lib/services/implementations/audio_service_impl.dart