Normalize Clerk organization admin roles to internal admin

Clerk namespaced admin roles now grant admin access — Roles returned by Clerk that include namespaces (for example `org:admin` or `org:owner`) are now normalized to the app's internal `admin` role so organization members receive the correct access and permissions.

Added a role-mapping function that normalizes Clerk membership roles (e.g., `org:admin`, `owner`) to the app's `admin` and `member` roles.auth

Updated webhook handlers so membership creation and updates use the new role mapping, ensuring members are assigned the correct admin/member role.backend
Added a fallback in the project creation flow: if creating a project for an organization is forbidden, the request now falls back to creating a personal project for the user instead of failing silently.frontend
Added an automated test to verify correct role mapping during membership.created events.backend

Updated backlog with prioritized proposals for explicit project owner selection and multi-organization membership behavior.