fix: rewrite FP workflow to use Ivanti multipart/form-data API

The /workflowBatch/falsePositive/request endpoint expects
multipart/form-data with text fields (name, reason, description,
expirationDate, overrideControl, subjectFilterRequest, isEmptyWorkflow)
and inline file uploads — not a JSON body with separate attachment calls.

- Add ivantiFormPost() helper for mixed form fields + files
- Replace buildIvantiPayload with buildIvantiFormFields + buildSubjectFilterRequest
- Remove separate attachment upload loop (files sent inline)
- Update response handling for { id, created } shape

backend/helpers/ivantiApi.js

@@ -88,4 +88,67 @@ function ivantiMultipartPost(urlPath, fileBuffer, fileName, apiKey, skipTls) {
     });
 }
 
-module.exports = { IVANTI_URL_BASE, ivantiPost, ivantiMultipartPost };
+// ---------------------------------------------------------------------------
+// Multipart form POST — used for endpoints that accept mixed form fields + files.
+// fields: array of { name, value } for text form fields
+// files:  array of { name, buffer, filename } for file uploads
+// ---------------------------------------------------------------------------
+function ivantiFormPost(urlPath, fields, files, apiKey, skipTls) {
+    const boundary = '----IvantiForm' + Date.now().toString(36) + Math.random().toString(36).slice(2);
+    const fullUrl = new URL(IVANTI_URL_BASE + urlPath);
+
+    const parts = [];
+
+    // Text fields
+    for (const { name, value } of fields) {
+        parts.push(Buffer.from(
+            `--${boundary}\r\n` +
+            `Content-Disposition: form-data; name="${name}"\r\n\r\n` +
+            `${value}\r\n`
+        ));
+    }
+
+    // File fields
+    for (const { name, buffer, filename } of files) {
+        parts.push(Buffer.from(
+            `--${boundary}\r\n` +
+            `Content-Disposition: form-data; name="${name}"; filename="${filename}"\r\n` +
+            `Content-Type: application/octet-stream\r\n\r\n`
+        ));
+        parts.push(buffer);
+        parts.push(Buffer.from('\r\n'));
+    }
+
+    parts.push(Buffer.from(`--${boundary}--\r\n`));
+    const bodyBuffer = Buffer.concat(parts);
+
+    return new Promise((resolve, reject) => {
+        const options = {
+            hostname: fullUrl.hostname,
+            path: fullUrl.pathname + fullUrl.search,
+            method: 'POST',
+            headers: {
+                'accept': '*/*',
+                'content-type': `multipart/form-data; boundary=${boundary}`,
+                'x-api-key': apiKey,
+                'x-http-client-type': 'browser',
+                'content-length': bodyBuffer.length
+            },
+            rejectUnauthorized: !skipTls,
+            timeout: 60000
+        };
+
+        const req = https.request(options, (res) => {
+            let data = '';
+            res.on('data', (chunk) => { data += chunk; });
+            res.on('end', () => resolve({ status: res.statusCode, body: data }));
+        });
+
+        req.on('timeout', () => req.destroy(new Error('Request timed out')));
+        req.on('error', reject);
+        req.write(bodyBuffer);
+        req.end();
+    });
+}
+
+module.exports = { IVANTI_URL_BASE, ivantiPost, ivantiMultipartPost, ivantiFormPost };