Add Mistral AI as inference provider with Voxtral Small transcription model

- Add support for multiple API providers (Groq and Mistral)
- Add collapsible API keys section in settings for both providers
- Label all models with their provider (Groq/Mistral)
- Add Voxtral Small (Mistral) transcription model
- Add Mistral Small and Mistral Medium AI refinement models
- Use user-friendly model names while maintaining correct API model values
- Update transcriber to route requests to correct provider based on model
- Update config to store separate API keys for each provider
- Add Mistral brand colors to CSS
- Style API keys dropdown section

Co-authored-by: jahruz67 <jahruz67@users.noreply.github.com>

internal/config/config.go

@@ -31,7 +31,8 @@ type HistoryItem struct {
 // Config represents the complete application configuration.
 type Config struct {
 	Version          int           `json:"version"`
-	APIKey           string        `json:"api_key"`
+	GroqAPIKey       string        `json:"groq_api_key"`
+	MistralAPIKey    string        `json:"mistral_api_key"`
 	Shortcut         string        `json:"shortcut"`
 	WhisperModel     string        `json:"whisper_model"`
 	AIModel          string        `json:"ai_model"`
@@ -50,7 +51,8 @@ var saveMu sync.Mutex
 // DefaultConfig returns a new configuration with sensible default values.
 func DefaultConfig() *Config {
 	return &Config{
-		APIKey:           "",
+		GroqAPIKey:       "",
+		MistralAPIKey:    "",
 		Shortcut:         DefaultShortcut,
 		WhisperModel:     DefaultWhisperModel,
 		AIModel:          DefaultAIModel,
@@ -197,3 +199,25 @@ func (c *Config) AddHistoryItem(text, timestamp string) {
 func (c *Config) ClearHistory() {
 	c.History = []HistoryItem{}
 }
+
+// GetAPIKey returns the API key for a specific provider
+func (c *Config) GetAPIKey(provider string) string {
+	switch provider {
+	case "groq":
+		return c.GroqAPIKey
+	case "mistral":
+		return c.MistralAPIKey
+	default:
+		return ""
+	}
+}
+
+// SetAPIKey sets the API key for a specific provider
+func (c *Config) SetAPIKey(provider, key string) {
+	switch provider {
+	case "groq":
+		c.GroqAPIKey = key
+	case "mistral":
+		c.MistralAPIKey = key
+	}
+}