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.controller.ts

@@ -0,0 +1,41 @@
+import { Body, Controller, Get, Param, Post, Query } from '@nestjs/common';
+import { ConversationService } from './conversation.service';
+
+@Controller('conversations')
+export class ConversationController {
+  constructor(private readonly conversationService: ConversationService) {}
+
+  @Get()
+  async getConversations(@Query('userId') userId: string) {
+    return this.conversationService.getConversations(userId);
+  }
+
+  @Get(':id')
+  async getConversation(@Param('id') id: string) {
+    return this.conversationService.getConversation(id);
+  }
+
+  @Get(':id/messages')
+  async getMessages(@Param('id') id: string) {
+    return this.conversationService.getMessages(id);
+  }
+
+  @Post()
+  async createConversation(
+    @Body() body: { userId: string; modelId: string; title?: string },
+  ) {
+    return this.conversationService.createConversation(
+      body.userId,
+      body.modelId,
+      body.title,
+    );
+  }
+
+  @Post(':id/messages')
+  async addMessage(
+    @Param('id') id: string,
+    @Body() body: { sender: 'user' | 'assistant' | 'system'; messageText: string },
+  ) {
+    return this.conversationService.addMessage(id, body.sender, body.messageText);
+  }
+}