feat: add file upload button to media library

- Added file upload button with multi-file support alongside existing paste functionality
- Implemented handleFileUpload function to process multiple image files sequentially
- Added file input reference and reset logic to allow repeated uploads
- Included upload progress indicator showing count of files being processed
- Added validation to skip non-image files with error messaging
- Enhanced UI with disabled state during upload to prevent concurrent

apps/admin/src/components/MediaLibrary.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useState } from 'react';
+import { useEffect, useMemo, useState, useRef } from 'react';
 import { Box, Button, Stack, Typography, Paper, TextField, MenuItem } from '@mui/material';
 
 type MediaItem = {
@@ -138,6 +138,42 @@ export default function MediaLibrary({
     } catch {}
   };
 
+  const fileInputRef = useRef<HTMLInputElement>(null);
+
+  const handleFileUpload = async (files: FileList | null) => {
+    if (!files || files.length === 0) return;
+    
+    setUploading(true);
+    setUploadingCount(files.length);
+    setError('');
+    
+    for (let i = 0; i < files.length; i++) {
+      const file = files[i];
+      if (!file.type.startsWith('image/')) {
+        setError(`Skipped ${file.name}: not an image`);
+        continue;
+      }
+      
+      try {
+        const fd = new FormData();
+        fd.append('image', file, file.name);
+        const res = await fetch('/api/media/image', { method: 'POST', body: fd });
+        if (!res.ok) throw new Error(await res.text());
+      } catch (err: any) {
+        setError(err?.message || `Failed to upload ${file.name}`);
+      }
+    }
+    
+    setUploading(false);
+    setUploadingCount(0);
+    await load();
+    
+    // Reset file input
+    if (fileInputRef.current) {
+      fileInputRef.current.value = '';
+    }
+  };
+
   return (
     <Paper sx={{ p: 2 }}>
       <Stack direction={{ xs: 'column', sm: 'row' }} justifyContent="flex-end" alignItems={{ xs: 'stretch', sm: 'center' }} sx={{ mb: 2, gap: 1 }}>
@@ -155,6 +191,22 @@ export default function MediaLibrary({
             <MenuItem value="name_asc">Name</MenuItem>
             <MenuItem value="size_desc">Largest</MenuItem>
           </TextField>
+          <input
+            ref={fileInputRef}
+            type="file"
+            accept="image/*"
+            multiple
+            style={{ display: 'none' }}
+            onChange={(e) => handleFileUpload(e.target.files)}
+          />
+          <Button 
+            size="small" 
+            variant="contained" 
+            onClick={() => fileInputRef.current?.click()}
+            disabled={uploading}
+          >
+            {uploading ? `Uploading ${uploadingCount}...` : 'Upload Images'}
+          </Button>
           <Button size="small" onClick={load} disabled={loading}>Refresh</Button>
           <Typography variant="caption" sx={{ color: 'text.secondary', display: { xs: 'none', md: 'block' } }}>
             Tip: paste an image (Cmd/Ctrl+V) to upload{uploading ? ` — uploading ${uploadingCount}…` : ''}