feat: add shared cross-platform catbox media upload flow

Added `useFileUpload()` and `uploadToCatbox()` to centralize upload behavior and remove duplicated upload code from `post-form.tsx` and `reply-modal.tsx`. The flow now routes Android to `FileUploader`, Electron to hidden-input + catbox upload, and web to a translated fallback alert with consistent upload UI state.

src/hooks/use-file-upload.ts

@@ -0,0 +1,104 @@
+import { useCallback, useState } from 'react';
+import { Capacitor } from '@capacitor/core';
+import { useTranslation } from 'react-i18next';
+import FileUploader from '../plugins/file-uploader';
+import { uploadToCatbox } from '../lib/utils/catbox-utils';
+
+const FILE_SELECTION_CANCELLED_ERROR = 'File selection cancelled';
+
+export interface UseFileUploadOptions {
+  onUploadComplete: (url: string, fileName: string) => void;
+}
+
+function selectFileViaInput(): Promise<File | null> {
+  return new Promise((resolve) => {
+    const input = document.createElement('input');
+    input.type = 'file';
+    input.accept = 'image/jpeg,image/png,video/mp4,video/webm';
+    input.style.display = 'none';
+
+    const cleanup = () => {
+      input.remove();
+      window.removeEventListener('focus', onFocus);
+    };
+
+    const onFocus = () => {
+      window.removeEventListener('focus', onFocus);
+      setTimeout(() => {
+        if (input.files && input.files.length > 0) {
+          return;
+        }
+        cleanup();
+        resolve(null);
+      }, 100);
+    };
+
+    input.addEventListener('change', () => {
+      window.removeEventListener('focus', onFocus);
+      if (input.files && input.files.length > 0) {
+        const file = input.files[0];
+        cleanup();
+        resolve(file);
+      } else {
+        cleanup();
+        resolve(null);
+      }
+    });
+
+    window.addEventListener('focus', onFocus);
+    document.body.appendChild(input);
+    input.click();
+  });
+}
+
+export function useFileUpload(options: UseFileUploadOptions) {
+  const { t } = useTranslation();
+  const { onUploadComplete } = options;
+  const [isUploading, setIsUploading] = useState(false);
+  const [uploadedFileName, setUploadedFileName] = useState<string | null>(null);
+
+  const handleUpload = useCallback(async () => {
+    try {
+      setIsUploading(true);
+      setUploadedFileName(null);
+
+      if (Capacitor.getPlatform() === 'android') {
+        const result = await FileUploader.pickAndUploadMedia();
+        if (result.url) {
+          if (result.fileName) {
+            setUploadedFileName(result.fileName);
+          }
+          onUploadComplete(result.url, result.fileName);
+        }
+        return;
+      }
+
+      if (window.electronApi?.isElectron) {
+        const file = await selectFileViaInput();
+        if (!file) {
+          throw new Error(FILE_SELECTION_CANCELLED_ERROR);
+        }
+
+        const url = await uploadToCatbox(file);
+        setUploadedFileName(file.name);
+        onUploadComplete(url, file.name);
+        return;
+      }
+
+      window.alert(t('upload_not_supported_web'));
+    } catch (error) {
+      const errorMessage = error instanceof Error ? error.message : String(error);
+      if (errorMessage !== FILE_SELECTION_CANCELLED_ERROR) {
+        window.alert(`${t('upload_failed')}: ${errorMessage}`);
+      }
+    } finally {
+      setIsUploading(false);
+    }
+  }, [onUploadComplete, t]);
+
+  return {
+    isUploading,
+    uploadedFileName,
+    handleUpload,
+  };
+}