refactor: 规范化页面组件目录结构

- 将 QrCodePreview、ImageUploader 移动到 QrCode/components/
- 将 DecodeResultPaper、Base64ConverterSection、TextMode 移动到 Base64Converter/components/
- 提取 useTextMode Hook，遵循 UI + Hook 分离模式
- 简化 SwitchButtonGroup 组件，提取常量到外部

Co-authored-by: Cursor <cursoragent@cursor.com>

src/pages/Base64Converter/useTextMode.ts

@@ -0,0 +1,95 @@
+import { useCallback, useEffect, useMemo, useState } from 'react';
+import { useI18n } from '@/utils/chromeI18n';
+import { base64ToText, textToBase64 } from '@/utils/base64Converter';
+import { useContextMenuData } from '@/utils/useContextMenuData';
+
+const IMAGE_DATA_URI_PATTERN = /^\s*data:image\//i;
+
+const ERROR_MESSAGE_TO_I18N: Record<string, string> = {
+  'Invalid Base64 string': 'invalidBase64',
+  'Input appears to be binary data (e.g. an image). Please use the Image tab instead.':
+    'binaryDataDetected',
+};
+
+export function useTextMode() {
+  const { t } = useI18n('base64Converter');
+
+  const [input, setInput] = useState('');
+  const [debouncedInput, setDebouncedInput] = useState('');
+  const [direction, setDirection] = useState<'encode' | 'decode'>('encode');
+
+  useEffect(() => {
+    const handle = setTimeout(() => {
+      setDebouncedInput(input);
+    }, 200);
+    return () => clearTimeout(handle);
+  }, [input]);
+
+  const handleContextMenuData = useCallback((payload: string) => {
+    setInput(payload);
+    setDebouncedInput(payload);
+    setDirection('decode');
+  }, []);
+
+  useContextMenuData({ featureKey: 'base64Converter', onData: handleContextMenuData });
+
+  const conversionPipeline = useMemo(() => {
+    const trimmed = debouncedInput.trim();
+    if (!trimmed) return { output: '', error: null };
+
+    try {
+      if (direction === 'encode') {
+        const result = textToBase64(debouncedInput);
+        return { output: result.output, error: null };
+      } else {
+        const decoded = base64ToText(trimmed);
+        return { output: decoded, error: null };
+      }
+    } catch (e) {
+      const message = e instanceof Error ? e.message : '';
+      const i18nKey = ERROR_MESSAGE_TO_I18N[message];
+      return {
+        output: '',
+        error: i18nKey ? t(i18nKey) : message || t('conversionFailed'),
+      };
+    }
+  }, [debouncedInput, direction, t]);
+
+  const output = conversionPipeline.output;
+  const error = conversionPipeline.error;
+
+  const placeholder =
+    direction === 'encode' ? t('textInputPlaceholder') : t('base64InputPlaceholder');
+  const outputLabel = direction === 'encode' ? t('base64Output') : t('textOutput');
+
+  const showImageHint = useMemo(
+    () => direction === 'decode' && IMAGE_DATA_URI_PATTERN.test(input),
+    [direction, input],
+  );
+
+  const handleDirectionChange = (value: 'encode' | 'decode') => {
+    if (value === direction) return;
+    setDirection(value);
+    setInput('');
+    setDebouncedInput('');
+  };
+
+  const handleClear = () => {
+    setInput('');
+    setDebouncedInput('');
+  };
+
+  return {
+    input,
+    setInput,
+    direction,
+    handleDirectionChange,
+    placeholder,
+    output,
+    outputLabel,
+    error,
+    showImageHint,
+    handleClear,
+    t,
+  };
+}