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_groq_translation.go

@@ -0,0 +1,63 @@
+package transcriber
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/sashabaranov/go-openai"
+)
+
+// GroqTranslationAdapter implements TranscriptionAdapter for Groq Translation API
+// Translates audio to English text. The Language field in config hints at the source language.
+type GroqTranslationAdapter struct {
+	client *openai.Client
+	config Config
+}
+
+func NewGroqTranslationAdapter(config Config) *GroqTranslationAdapter {
+	clientConfig := openai.DefaultConfig(config.APIKey)
+	clientConfig.BaseURL = "https://api.groq.com/openai/v1"
+	client := openai.NewClientWithConfig(clientConfig)
+
+	return &GroqTranslationAdapter{
+		client: client,
+		config: config,
+	}
+}
+
+func (a *GroqTranslationAdapter) Transcribe(ctx context.Context, audioData []byte) (string, error) {
+	if len(audioData) == 0 {
+		return "", nil
+	}
+
+	// Convert raw PCM to WAV format
+	wavData, err := convertToWAV(audioData)
+	if err != nil {
+		return "", fmt.Errorf("convert to WAV: %w", err)
+	}
+
+	// Create translation request
+	// Note: Translation always outputs English, regardless of target language
+	// The Language field in the request hints at the source audio language for better accuracy
+	req := openai.AudioRequest{
+		Model:    a.config.Model,
+		Reader:   bytes.NewReader(wavData),
+		FilePath: "audio.wav",
+		Language: a.config.Language, // Source language hint
+	}
+
+	start := time.Now()
+	resp, err := a.client.CreateTranslation(ctx, req)
+	duration := time.Since(start)
+
+	if err != nil {
+		log.Printf("groq-translation-adapter: API call failed after %v: %v", duration, err)
+		return "", fmt.Errorf("groq translation: %w", err)
+	}
+
+	log.Printf("groq-translation-adapter: translated %d bytes in %v: %q", len(audioData), duration, resp.Text)
+	return resp.Text, nil
+}