Squashed for rebase — original commits:
- feat(desktop): add persona event kind with client publish/read/retain
- fix(desktop): sign every migrated persona event and drop the sentinel file
- fix(relay): validate kind:30175 persona d-tag slug grammar on ingest
- fix(desktop): drop env_vars from public PersonaEventContent
- docs: add NIP-AP spec for kind:30175 persona events
- feat(ci): add relay E2E testing job and persona event tests
