feat: QR 预览 + 导出面板(PNG/SVG/复制) + 文本/URL 模式

gui/src-frontend/src/modes/TextMode.tsx

@@ -0,0 +1,22 @@
+import { useQrState } from '../store/qrContext';
+import { useQrEncode } from '../hooks/useQrEncode';
+
+export default function TextMode() {
+  const { state, dispatch } = useQrState();
+  const { encode } = useQrEncode();
+
+  const handleChange = (text: string) => {
+    dispatch({ type: 'SET_FORM_DATA', payload: { text } });
+    encode(text);
+  };
+
+  return (
+    <textarea
+      placeholder="输入任意文本..."
+      value={state.formData.text || ''}
+      onChange={e => handleChange(e.target.value)}
+      rows={3}
+      className="w-full h-full resize-none px-4 py-2 text-sm bg-transparent outline-none placeholder-gray-400 dark:placeholder-gray-600"
+    />
+  );
+}

gui/src-frontend/src/modes/UrlMode.tsx

@@ -0,0 +1,32 @@
+import { useQrState } from '../store/qrContext';
+import { useQrEncode } from '../hooks/useQrEncode';
+
+export default function UrlMode() {
+  const { state, dispatch } = useQrState();
+  const { encode } = useQrEncode();
+
+  const handleChange = (url: string) => {
+    dispatch({ type: 'SET_FORM_DATA', payload: { url } });
+    encode(url);
+  };
+
+  const handleBlur = () => {
+    const url = state.formData.url || '';
+    if (url && !/^https?:\/\//i.test(url)) {
+      const corrected = `https://${url}`;
+      dispatch({ type: 'SET_FORM_DATA', payload: { url: corrected } });
+      encode(corrected);
+    }
+  };
+
+  return (
+    <input
+      type="url"
+      placeholder="https://example.com"
+      value={state.formData.url || ''}
+      onChange={e => handleChange(e.target.value)}
+      onBlur={handleBlur}
+      className="w-full h-full px-4 text-sm bg-transparent outline-none placeholder-gray-400 dark:placeholder-gray-600"
+    />
+  );
+}