feat(api): add break-glass local authentication module (#559)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/api/src/auth/local/local-auth.guard.ts

@@ -0,0 +1,15 @@
+import { Injectable, CanActivate, NotFoundException } from "@nestjs/common";
+
+/**
+ * Guard that checks if local authentication is enabled via ENABLE_LOCAL_AUTH env var.
+ * Returns 404 when disabled so endpoints are invisible to callers.
+ */
+@Injectable()
+export class LocalAuthEnabledGuard implements CanActivate {
+  canActivate(): boolean {
+    if (process.env.ENABLE_LOCAL_AUTH !== "true") {
+      throw new NotFoundException();
+    }
+    return true;
+  }
+}