Fix 's is not defined' in AIChatPanel

Leftover reference to removed 's' variable — changed to $settings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/components/AIChatPanel.svelte

@@ -50,7 +50,7 @@
       const result = await invoke<{ response: string }>('ai_chat', {
         messages: chatMessages,
         transcriptContext: getTranscriptContext(),
-        provider: s.ai_provider,
+        provider: $settings.ai_provider,
       });
 
       messages = [...messages, { role: 'assistant', content: result.response }];