Improve transcription accuracy with overlapping audio chunks

Changes:
1. Changed UI text from "Recording" to "Transcribing" for clarity
2. Implemented overlapping audio chunks to prevent word cutoff

Audio Overlap Feature:
- Added overlap_duration parameter (default: 0.5 seconds)
- Audio chunks now overlap by 0.5s to capture words at boundaries
- Prevents missed words when chunks are processed separately
- Configurable via audio.overlap_duration in config.yaml

How it works:
- Each 3-second chunk includes 0.5s from the previous chunk
- Buffer advances by (chunk_size - overlap_size) instead of full chunk
- Ensures words at chunk boundaries are captured in at least one chunk
- No duplicate transcription due to Whisper's context handling

Example with 3s chunks and 0.5s overlap:
  Chunk 1: [0.0s - 3.0s]
  Chunk 2: [2.5s - 5.5s]  <- 0.5s overlap
  Chunk 3: [5.0s - 8.0s]  <- 0.5s overlap

Files modified:
- client/audio_capture.py: Implemented overlapping buffer logic
- config/default_config.yaml: Added overlap_duration setting
- gui/main_window_qt.py: Updated UI text, passed overlap param
- main_cli.py: Passed overlap param

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

config/default_config.yaml

@@ -6,6 +6,7 @@ audio:
   input_device: "default"
   sample_rate: 16000
   chunk_duration: 3.0
+  overlap_duration: 0.5  # Overlap between chunks to prevent word cutoff (seconds)
 
 noise_suppression:
   enabled: true