Role defaults should not reference playbook-level variables like
matrix_playbook_reverse_proxy_type or traefik_entrypoint_primary,
as this breaks standalone usage of the role.

Following the pattern established by other roles (matrix-sliding-sync,
matrix-synapse-admin, matrix-media-repo, etc.), Traefik variables now
use safe standalone defaults (true, web-secure, default) while the
actual playbook wiring remains in group_vars/matrix_servers.

Also standardized certResolver variable naming to use camelCase,
consistent with other roles in the playbook.