Increase team-provisioner timeout to 300s (#124)

## Summary
- Increases team-provisioner Lambda timeout from 60s to 300s
- With 54 members, the Lambda timed out during group sync after creating
all accounts
- Each member takes ~3s (check exists + create + forwarding attempt +
welcome email), so 54 members alone need ~162s before group sync even
starts

## Context
The provision-groups run from registry PR #21 merge timed out at 60s.
All accounts were created and welcome emails sent, but group membership
sync didn't complete.

Author: Alexanderamiri

terraform/platform/lambdas/main.tf

@@ -887,7 +887,7 @@ resource "aws_lambda_function" "team_provisioner" {
   role             = aws_iam_role.team_provisioner.arn
   handler          = "handler.handler"
   runtime          = "python3.12"
-  timeout          = 60
+  timeout          = 300
   memory_size      = 256
   filename         = data.archive_file.team_provisioner.output_path
   source_code_hash = data.archive_file.team_provisioner.output_base64sha256