feat: Story 14 - Auto-focus chat input on startup

Implemented Story 14: Auto-focus Chat Input
- Added inputRef using useRef<HTMLInputElement>
- Added useEffect to focus input on component mount
- Input now automatically receives focus when chat loads
- Cursor is visible and blinking immediately
- Users can start typing without clicking into the field

Updated Specs
- Added Input Focus Management section to UI_UX.md
- Specified auto-focus behavior and requirements
- Provided implementation example

src/components/Chat.tsx

@@ -19,6 +19,7 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
   const [enableTools, setEnableTools] = useState(true);
   const [availableModels, setAvailableModels] = useState<string[]>([]);
   const messagesEndRef = useRef<HTMLDivElement>(null);
+  const inputRef = useRef<HTMLInputElement>(null);
 
   useEffect(() => {
     invoke<string[]>("get_ollama_models")
@@ -61,6 +62,10 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
 
   useEffect(scrollToBottom, [messages]);
 
+  useEffect(() => {
+    inputRef.current?.focus();
+  }, []);
+
   const sendMessage = async () => {
     if (!input.trim() || loading) return;
 
@@ -454,6 +459,7 @@ export function Chat({ projectPath, onCloseProject }: ChatProps) {
           }}
         >
           <input
+            ref={inputRef}
             value={input}
             onChange={(e) => setInput(e.target.value)}
             onKeyDown={(e) => e.key === "Enter" && sendMessage()}