These IDs were incorrectly auto-derived from matrix_homeserver_generic_secret_key,
which is meant for secrets that are OK to change. Datastore IDs are static
identifiers that must never change after first use.

The playbook now requires users to explicitly set matrix_media_repo_datastore_file_id
(and matrix_media_repo_datastore_s3_id when S3 is enabled) in vars.yml, with
validation that fails early if they are missing.

This was the last usage of passlib, which is now removed from prerequisites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>