Fix AI chat conversation errors and history loading issues

- Fix CircularProgress import from correct MUI package
- Fix conversationId validation by omitting null values instead of sending them
- Fix conversations API Zod schema default values (string vs number mismatch)
- Remove debug logging from chat error handling
- AI chat conversations now work properly with authentication
- Chat history loading no longer fails with validation errors

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/api/chat/conversations/route.ts

@@ -14,8 +14,8 @@ const createConversationSchema = z.object({
 
 const getConversationsSchema = z.object({
   language: z.enum(['ro', 'en']).optional(),
-  limit: z.string().transform(Number).pipe(z.number().min(1).max(50)).optional().default(20),
-  offset: z.string().transform(Number).pipe(z.number().min(0)).optional().default(0),
+  limit: z.string().transform(Number).pipe(z.number().min(1).max(50)).optional().default('20'),
+  offset: z.string().transform(Number).pipe(z.number().min(0)).optional().default('0'),
 })
 
 // GET /api/chat/conversations - List user's conversations