fix: resolve Groq STT key from model_list when providers.groq is absent (#602)

When users migrate from the legacy `providers` config to the new
`model_list` format, voice transcription silently breaks on Telegram,
Discord and Slack channels.

The gateway was reading the Groq API key exclusively from
`cfg.Providers.Groq.APIKey`, which is empty once the key is defined
only inside a `model_list` entry. The transcriber was never initialized,
so voice messages fell back to a plain `[voice]` placeholder.

This fix also scans `model_list` for any entry whose `model` field
starts with `groq/` and uses its `api_key` as a fallback, preserving
full backward compatibility with the legacy `providers.groq` field.

cmd/picoclaw/cmd_gateway.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/sipeed/picoclaw/pkg/agent"
@@ -121,8 +122,17 @@ func gatewayCmd() {
 	agentLoop.SetChannelManager(channelManager)
 
 	var transcriber *voice.GroqTranscriber
-	if cfg.Providers.Groq.APIKey != "" {
-		transcriber = voice.NewGroqTranscriber(cfg.Providers.Groq.APIKey)
+	groqAPIKey := cfg.Providers.Groq.APIKey
+	if groqAPIKey == "" {
+		for _, mc := range cfg.ModelList {
+			if strings.HasPrefix(mc.Model, "groq/") && mc.APIKey != "" {
+				groqAPIKey = mc.APIKey
+				break
+			}
+		}
+	}
+	if groqAPIKey != "" {
+		transcriber = voice.NewGroqTranscriber(groqAPIKey)
 		logger.InfoC("voice", "Groq voice transcription enabled")
 	}