design: implement multi-file selection support for research and existing-project onboarding uploaders

vibn-frontend/_onboarding/onboarding-entrepreneur.tsx

@@ -211,9 +211,14 @@ function EntrepResearch({ files = [], brief = "", onChange }) {
   const [progress, setProgress] = useState(0);
 
   const handleFileChange = (e: React.ChangeEvent<HTMLInputElement>) => {
-    const selected = e.target.files?.[0];
-    if (!selected) return;
-    setUploading(selected.name);
+    const selectedFiles = Array.from(e.target.files ?? []);
+    if (selectedFiles.length === 0) return;
+
+    const label =
+      selectedFiles.length === 1
+        ? selectedFiles[0].name
+        : `${selectedFiles.length} files`;
+    setUploading(label);
     setProgress(0);
 
     // Simulate a smooth upload progress bar
@@ -222,14 +227,12 @@ function EntrepResearch({ files = [], brief = "", onChange }) {
         if (p >= 100) {
           clearInterval(interval);
           setTimeout(() => {
+            const newFiles = selectedFiles.map((f) => ({
+              name: f.name,
+              size: `${(f.size / 1024).toFixed(1)} KB`,
+            }));
             onChange({
-              files: [
-                ...files,
-                {
-                  name: selected.name,
-                  size: `${(selected.size / 1024).toFixed(1)} KB`,
-                },
-              ],
+              files: [...files, ...newFiles],
             });
             setUploading(null);
           }, 300);
@@ -287,6 +290,7 @@ function EntrepResearch({ files = [], brief = "", onChange }) {
             <input
               type="file"
               onChange={handleFileChange}
+              multiple
               style={{ display: "none" }}
             />
             {uploading ? (
@@ -473,8 +477,9 @@ function EntrepExisting({ checklist = {}, onChange }) {
     key: "designs" | "code",
     e: React.ChangeEvent<HTMLInputElement>,
   ) => {
-    const selected = e.target.files?.[0];
-    if (!selected) return;
+    const selectedFiles = Array.from(e.target.files ?? []);
+    if (selectedFiles.length === 0) return;
+
     setUploading(key);
     setProgress(0);
 
@@ -484,16 +489,14 @@ function EntrepExisting({ checklist = {}, onChange }) {
           clearInterval(interval);
           setTimeout(() => {
             const currentFiles = checklist[`${key}Files`] || [];
+            const newFiles = selectedFiles.map((f) => ({
+              name: f.name,
+              size: `${(f.size / 1024).toFixed(1)} KB`,
+            }));
             onChange({
               checklist: {
                 ...checklist,
-                [`${key}Files`]: [
-                  ...currentFiles,
-                  {
-                    name: selected.name,
-                    size: `${(selected.size / 1024).toFixed(1)} KB`,
-                  },
-                ],
+                [`${key}Files`]: [...currentFiles, ...newFiles],
               },
             });
             setUploading(null);
@@ -546,6 +549,7 @@ function EntrepExisting({ checklist = {}, onChange }) {
           <input
             type="file"
             onChange={(e) => handleFileChange(key, e)}
+            multiple
             style={{ display: "none" }}
           />
           {uploading === key ? (