Switch file upload to proxy through backend instead of SAS URLs

Storage has publicNetworkAccess disabled, so browser cannot PUT directly
to blob storage via SAS URLs. Changed frontend to POST files as multipart
form data to /api/datasets/{dataset}/upload, which proxies through the
backend over the private endpoint.

Author: kmavrodis

frontend-next/src/lib/api-client.ts

@@ -447,37 +447,43 @@ class BackendClient {
     })
   }
 
-  // File upload with options - uses SAS URL for production
+  // File upload with options - proxies through backend to blob storage
   async uploadFile(
     datasetName: string,
     file: File,
     options?: UploadOptions
   ): Promise<{ message: string; id: string }> {
-    // Get SAS URL for direct blob upload
-    const uploadInfo = await this.getUploadUrl(file.name, datasetName)
-    
-    // Determine content type
-    const contentType = file.type || 'application/octet-stream'
-    
-    // Upload directly to Azure Blob Storage using SAS URL
-    const uploadResponse = await fetch(uploadInfo.upload_url, {
-      method: 'PUT',
-      headers: {
-        'x-ms-blob-type': 'BlockBlob',
-        'Content-Type': contentType,
-      },
-      body: file,
+    await this.initialize()
+
+    const formData = new FormData()
+    formData.append('file', file)
+
+    // Build query params for processing options
+    const params = new URLSearchParams()
+    if (options) {
+      if (options.run_ocr !== undefined) params.set('run_ocr', String(options.run_ocr))
+      if (options.run_gpt_vision !== undefined) params.set('run_gpt_vision', String(options.run_gpt_vision))
+      if (options.run_summary !== undefined) params.set('run_summary', String(options.run_summary))
+      if (options.run_evaluation !== undefined) params.set('run_evaluation', String(options.run_evaluation))
+    }
+
+    const queryString = params.toString()
+    const url = `${this.baseUrl}/api/datasets/${encodeURIComponent(datasetName)}/upload${queryString ? `?${queryString}` : ''}`
+
+    const response = await fetch(url, {
+      method: 'POST',
+      body: formData,
     })
 
-    if (!uploadResponse.ok) {
-      const errorText = await uploadResponse.text().catch(() => '')
-      throw new Error(`Upload failed: ${uploadResponse.status} ${errorText}`)
+    if (!response.ok) {
+      const errorData = await response.json().catch(() => ({}))
+      throw new Error(errorData.detail || `Upload failed: ${response.status}`)
     }
 
-    // The blob upload triggers automatic processing via Event Grid
+    const result = await response.json()
     return {
-      message: `File ${file.name} uploaded successfully to ${datasetName}. Processing will begin automatically.`,
-      id: uploadInfo.blob_path,
+      message: result.message || `File ${file.name} uploaded successfully to ${datasetName}. Processing will begin automatically.`,
+      id: result.document_id || result.blob_path || '',
     }
   }