AgentMBX v0.5.3

What's Changed

• docs(T156): session catch-up spec — durable consumer checkpoints per identity by @kryptobaseddev in #61
• feat(S1): self-healing skill, skills-CLI aware, and the guide over MCP by @kryptobaseddev in #64
• fix(S2): no phantom mailboxes from received mail; doctor --fix; return to sender by @kryptobaseddev in #63
• fix(S1): write the skill atomically (temp file + rename) by @kryptobaseddev in #66
• feat(T157/T158): durable consumer checkpoints per identity, mbx_catchup by @kryptobaseddev in #62
• feat(T218/T219): signed cross-host receipts and a cross-host project ledger by @kryptobaseddev in #65
• release(T215): v0.5.3 by @kryptobaseddev in #67

Full Changelog: v0.5.2...v0.5.3