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/apps/mobile/hooks/useChatInput.ts

@@ -0,0 +1,50 @@
+import { useState } from 'react';
+import { useAppTheme } from '../theme/ThemeProvider';
+
+interface UseChatInputProps {
+  onSend: (message: string) => void;
+  isLoading?: boolean;
+  initialText?: string;
+  placeholder?: string;
+  maxLength?: number;
+}
+
+interface UseChatInputReturn {
+  text: string;
+  setText: (text: string) => void;
+  handleSend: () => void;
+  canSend: boolean;
+  isLoading: boolean;
+  isDarkMode: boolean;
+  placeholder: string;
+}
+
+export default function useChatInput({
+  onSend,
+  isLoading = false,
+  initialText = '',
+  placeholder = 'Nachricht eingeben...',
+  maxLength = 1000,
+}: UseChatInputProps): UseChatInputReturn {
+  const [text, setText] = useState(initialText);
+  const { isDarkMode } = useAppTheme();
+  
+  const canSend = text.trim().length > 0 && !isLoading;
+  
+  const handleSend = () => {
+    if (canSend) {
+      onSend(text.trim());
+      setText('');
+    }
+  };
+  
+  return {
+    text,
+    setText,
+    handleSend,
+    canSend,
+    isLoading,
+    isDarkMode,
+    placeholder,
+  };
+}