Split SimpleFIN connections by institution

Group discovered SimpleFIN accounts by institution and create a
separate SyncConnection per institution so each bank appears as
its own card in the UI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/settings/SettingsView.vue

@@ -728,12 +728,16 @@ function loadPlaidScript(): Promise<void> {
 async function connectSimpleFin() {
   simpleFinLoading.value = true
   try {
-    const { data: conn } = await bankSyncApi.connectSimpleFin(simpleFinToken.value)
-    connections.value.unshift(conn)
-    syncIntervals[conn.id] = conn.syncIntervalMinutes
+    const { data: newConnections } = await bankSyncApi.connectSimpleFin(simpleFinToken.value)
+    for (const conn of newConnections) {
+      connections.value.unshift(conn)
+      syncIntervals[conn.id] = conn.syncIntervalMinutes
+    }
     showSimpleFinDialog.value = false
     simpleFinToken.value = ''
-    openMappingDialog(conn)
+    if (newConnections.length > 0) {
+      openMappingDialog(newConnections[0])
+    }
   } catch (err: any) {
     errorMessage.value = err.response?.data?.error || 'Failed to connect via SimpleFIN. Check your setup token.'
     showError.value = true