fix(ui): useApi passes FormData through unaltered so multipart uploads work (IR/GS ingest from UI was JSON-stringifying FormData into '{}')

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/composables/useApi.js

@@ -24,8 +24,16 @@ async function request(method, url, { body, params, signal } = {}) {
   const headers = {}
   const init = { method, headers, signal }
   if (body !== undefined) {
-    headers['Content-Type'] = 'application/json'
-    init.body = JSON.stringify(body)
+    if (body instanceof FormData) {
+      // Let the browser set Content-Type with the multipart boundary.
+      // JSON-stringifying FormData produces "{}" and the backend sees
+      // an empty multipart payload (this broke FC-5 IR/GS ingest from
+      // the UI for several releases).
+      init.body = body
+    } else {
+      headers['Content-Type'] = 'application/json'
+      init.body = JSON.stringify(body)
+    }
   }
 
   const r = await fetch(fullUrl, init)