fix: set user_id in context for service account auth path to prevent panic on project creation

[nimish22]

This is fix for issue #180

---

Summary by cubic

Prevents a panic during project creation with service account auth by setting missing context values and making getters safe. Fixes #180.

• Bug Fixes
  • Set user_id, user_role, and user_email in the service account path in RequireAuth; also set user_email for standard and OAuth auth to keep context keys consistent.
  • Update BaseHandler getters to use safe string assertions and read user_role; add regression tests to ensure they don't panic when context values are missing.

^{Written for commit e7ca68e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

[cwrm56]

Claude suggests adding "a specific test for the service account project creation path — there's no test that sets up a service account context (with is_service_account=true and user_id set) and calls the project creation handler to verify it doesn't panic."
But I have approved.

[nimish22]

Claude suggests adding "a specific test for the service account project creation path — there's no test that sets up a service account context (with is_service_account=true and user_id set) and calls the project creation handler to verify it doesn't panic." But I have approved.

Added tests as suggested.