fix: pass language parameter to Qwen TTS models and sync form with profile language

Both PyTorch and MLX backends silently dropped the language parameter —
it was accepted by generate() but never forwarded to the underlying
Qwen3-TTS model, causing it to default to auto-detection which
frequently confuses similar languages (e.g. Portuguese for Spanish).

- Add LANGUAGE_CODE_TO_NAME mapping (ISO 639-1 to full name) to both backends
- PyTorch: pass language= to generate_voice_clone()
- MLX: pass lang_code= to all 4 model.generate() call sites
- Frontend: auto-sync generation form language with selected voice profile

Closes #97

app/src/components/Generation/FloatingGenerateBox.tsx

@@ -13,7 +13,7 @@ import {
 } from '@/components/ui/select';
 import { Textarea } from '@/components/ui/textarea';
 import { useToast } from '@/components/ui/use-toast';
-import { getLanguageOptionsForEngine } from '@/lib/constants/languages';
+import { getLanguageOptionsForEngine, type LanguageCode } from '@/lib/constants/languages';
 import { useGenerationForm } from '@/lib/hooks/useGenerationForm';
 import { useProfile, useProfiles } from '@/lib/hooks/useProfiles';
 import { useAddStoryItem, useStory } from '@/lib/hooks/useStories';
@@ -112,6 +112,13 @@ export function FloatingGenerateBox({
     }
   }, [selectedProfileId, profiles, setSelectedProfileId]);
 
+  // Sync generation form language with selected profile's language
+  useEffect(() => {
+    if (selectedProfile?.language) {
+      form.setValue('language', selectedProfile.language as LanguageCode);
+    }
+  }, [selectedProfile, form]);
+
   // Auto-resize textarea based on content (only when expanded)
   useEffect(() => {
     if (!isExpanded) {
@@ -344,9 +351,7 @@ export function FloatingGenerateBox({
                               : 'bg-card border border-border hover:bg-background/50',
                           )}
                           aria-label={
-                            isInstructMode
-                              ? 'Fine tune instructions, on'
-                              : 'Fine tune instructions'
+                            isInstructMode ? 'Fine tune instructions, on' : 'Fine tune instructions'
                           }
                         >
                           <SlidersHorizontal className="h-4 w-4" />