feat(chat): integrate chat project into monorepo with full app structure

- Restructure chat as apps/mobile, apps/web, apps/landing, backend
- Add NestJS backend for secure Azure OpenAI API calls
- Remove exposed API key from mobile app (security fix)
- Add shared chat-types package
- Create SvelteKit web app scaffold
- Create Astro landing page scaffold
- Update pnpm workspace configuration
- Add project-level CLAUDE.md documentation

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

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

chat/backend/src/conversation/conversation.service.ts

@@ -0,0 +1,158 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { createClient, SupabaseClient } from '@supabase/supabase-js';
+
+export interface Conversation {
+  id: string;
+  user_id: string;
+  model_id: string;
+  title?: string;
+  is_archived: boolean;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface Message {
+  id: string;
+  conversation_id: string;
+  sender: 'user' | 'assistant' | 'system';
+  message_text: string;
+  created_at: string;
+}
+
+@Injectable()
+export class ConversationService {
+  private readonly logger = new Logger(ConversationService.name);
+  private supabase: SupabaseClient;
+
+  constructor(private configService: ConfigService) {
+    const supabaseUrl = this.configService.get<string>('SUPABASE_URL');
+    const supabaseKey = this.configService.get<string>('SUPABASE_SERVICE_KEY');
+
+    if (supabaseUrl && supabaseKey) {
+      this.supabase = createClient(supabaseUrl, supabaseKey);
+    } else {
+      this.logger.warn('Supabase configuration missing');
+    }
+  }
+
+  async getConversations(userId: string): Promise<Conversation[]> {
+    if (!this.supabase) {
+      this.logger.warn('Supabase not configured');
+      return [];
+    }
+
+    const { data, error } = await this.supabase
+      .from('conversations')
+      .select('*')
+      .eq('user_id', userId)
+      .eq('is_archived', false)
+      .order('updated_at', { ascending: false });
+
+    if (error) {
+      this.logger.error('Error fetching conversations', error);
+      throw error;
+    }
+
+    return data || [];
+  }
+
+  async getConversation(id: string): Promise<Conversation | null> {
+    if (!this.supabase) {
+      return null;
+    }
+
+    const { data, error } = await this.supabase
+      .from('conversations')
+      .select('*')
+      .eq('id', id)
+      .single();
+
+    if (error) {
+      this.logger.error('Error fetching conversation', error);
+      return null;
+    }
+
+    return data;
+  }
+
+  async getMessages(conversationId: string): Promise<Message[]> {
+    if (!this.supabase) {
+      return [];
+    }
+
+    const { data, error } = await this.supabase
+      .from('messages')
+      .select('*')
+      .eq('conversation_id', conversationId)
+      .order('created_at', { ascending: true });
+
+    if (error) {
+      this.logger.error('Error fetching messages', error);
+      throw error;
+    }
+
+    return data || [];
+  }
+
+  async createConversation(
+    userId: string,
+    modelId: string,
+    title?: string,
+  ): Promise<Conversation> {
+    if (!this.supabase) {
+      throw new Error('Supabase not configured');
+    }
+
+    const { data, error } = await this.supabase
+      .from('conversations')
+      .insert({
+        user_id: userId,
+        model_id: modelId,
+        title: title || 'Neue Unterhaltung',
+        is_archived: false,
+      })
+      .select()
+      .single();
+
+    if (error) {
+      this.logger.error('Error creating conversation', error);
+      throw error;
+    }
+
+    return data;
+  }
+
+  async addMessage(
+    conversationId: string,
+    sender: 'user' | 'assistant' | 'system',
+    messageText: string,
+  ): Promise<Message> {
+    if (!this.supabase) {
+      throw new Error('Supabase not configured');
+    }
+
+    const { data, error } = await this.supabase
+      .from('messages')
+      .insert({
+        conversation_id: conversationId,
+        sender,
+        message_text: messageText,
+      })
+      .select()
+      .single();
+
+    if (error) {
+      this.logger.error('Error adding message', error);
+      throw error;
+    }
+
+    // Update conversation updated_at
+    await this.supabase
+      .from('conversations')
+      .update({ updated_at: new Date().toISOString() })
+      .eq('id', conversationId);
+
+    return data;
+  }
+}