Previously, SSH key fingerprints were globally unique across all users,
preventing the same key from being registered by different users. This
change makes fingerprint uniqueness scoped to individual users.
- Remove global unique constraints on payload and fingerprint columns
- Add composite unique constraint on (user_id, fingerprint)
- Make add_ssh_key operation idempotent for same user
- Return tuple (SSHKey, is_new) from service to indicate creation status
- Update API to return 200 for existing keys, 201 for new keys
BREAKING CHANGE: API behavior changed - duplicate key addition now
returns 200 OK instead of 409 Conflict. Service method signature changed
from returning SSHKey to tuple[SSHKey, bool].
nexgen_mirrors
de6f39e7e3