Release v0.28.12

What's Changed

• fix(headless): rebuild stale approval input on resync by @jnjpng in #3403
• fix(slack): hide generic tool activity from status by @cpacker in #3408
• feat(skills): add self-configuration skill by @overlord-letta in #3401
• feat(cli): unify App Server under letta server by @cpacker in #3415
• fix(cli): expose cloud as the backend name by @cpacker in #3416
• chore: bump version to 0.28.12 by @github-actions[bot] in #3417

Full Changelog: v0.28.11...v0.28.12