feat: add Groq Whisper API support for transcription and translation

Add support for Groq Whisper API as an alternative to OpenAI:
- groq-transcription: Fast transcription using whisper-large-v3 or whisper-large-v3-turbo
- groq-translation: Translation to English (whisper-large-v3 only)

Features:
- New transcription adapters for both Groq services
- Config validation with provider-specific model restrictions
- API key support via config file or GROQ_API_KEY environment variable
- Updated interactive configuration wizard with provider selection
- Comprehensive test coverage for all providers
- Shared WAV conversion utility for audio preprocessing

Breaking changes: None
Backward compatibility: Existing OpenAI configurations continue to work unchanged

internal/transcriber/adapter_openai.go

@@ -3,7 +3,6 @@ package transcriber
 import (
 	"bytes"
 	"context"
-	"encoding/binary"
 	"fmt"
 	"log"
 	"time"
@@ -31,7 +30,7 @@ func (a *OpenAIAdapter) Transcribe(ctx context.Context, audioData []byte) (strin
 	}
 
 	// Convert raw PCM to WAV format
-	wavData, err := a.convertToWAV(audioData)
+	wavData, err := convertToWAV(audioData)
 	if err != nil {
 		return "", fmt.Errorf("convert to WAV: %w", err)
 	}
@@ -56,39 +55,3 @@ func (a *OpenAIAdapter) Transcribe(ctx context.Context, audioData []byte) (strin
 	log.Printf("openai-adapter: transcribed %d bytes in %v: %q", len(audioData), duration, resp.Text)
 	return resp.Text, nil
 }
-
-// convertToWAV converts raw 16-bit PCM audio to WAV format
-func (a *OpenAIAdapter) convertToWAV(rawAudio []byte) ([]byte, error) {
-	var buf bytes.Buffer
-
-	const sampleRate = 16000
-	const channels = 1
-	const bitsPerSample = 16
-	const byteRate = sampleRate * channels * bitsPerSample / 8
-	const blockAlign = channels * bitsPerSample / 8
-
-	dataSize := len(rawAudio)
-	fileSize := 36 + dataSize
-
-	// WAV header
-	buf.WriteString("RIFF")
-	binary.Write(&buf, binary.LittleEndian, uint32(fileSize))
-	buf.WriteString("WAVE")
-
-	// fmt chunk
-	buf.WriteString("fmt ")
-	binary.Write(&buf, binary.LittleEndian, uint32(16))            // fmt chunk size
-	binary.Write(&buf, binary.LittleEndian, uint16(1))             // PCM format
-	binary.Write(&buf, binary.LittleEndian, uint16(channels))      // number of channels
-	binary.Write(&buf, binary.LittleEndian, uint32(sampleRate))    // sample rate
-	binary.Write(&buf, binary.LittleEndian, uint32(byteRate))      // byte rate
-	binary.Write(&buf, binary.LittleEndian, uint16(blockAlign))    // block align
-	binary.Write(&buf, binary.LittleEndian, uint16(bitsPerSample)) // bits per sample
-
-	// data chunk
-	buf.WriteString("data")
-	binary.Write(&buf, binary.LittleEndian, uint32(dataSize))
-	buf.Write(rawAudio)
-
-	return buf.Bytes(), nil
-}