Add Node.js backend API with mock providers for all 15 vendors

Express app on port 3000 with /api/status and /api/health endpoints.
Polls all providers every 2 minutes and caches results in memory.
Each vendor is a self-contained ESM module with 10s timeout and
graceful failure handling. Mock data matches existing frontend.

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

backend/providers/index.js

@@ -0,0 +1,33 @@
+import * as microsoft365 from "./microsoft365.js";
+import * as spamtitan from "./spamtitan.js";
+import * as powerschool from "./powerschool.js";
+import * as classlink from "./classlink.js";
+import * as apple from "./apple.js";
+import * as drc from "./drc.js";
+import * as finalsite from "./finalsite.js";
+import * as googleWorkspace from "./google-workspace.js";
+import * as follett from "./follett.js";
+import * as edinsight from "./edinsight.js";
+import * as raptor from "./raptor.js";
+import * as schoolmessenger from "./schoolmessenger.js";
+import * as fortinet from "./fortinet.js";
+import * as mcgrawHill from "./mcgraw-hill.js";
+import * as localInfrastructure from "./local-infrastructure.js";
+
+export const providers = [
+  microsoft365,
+  spamtitan,
+  powerschool,
+  classlink,
+  apple,
+  drc,
+  finalsite,
+  googleWorkspace,
+  follett,
+  edinsight,
+  raptor,
+  schoolmessenger,
+  fortinet,
+  mcgrawHill,
+  localInfrastructure,
+];