v0.9.81 — AgentMail email connect error handling

• Return a CORS-safe 409 agentmail_inbox_limit response when AgentMail refuses inbox creation because the inbox quota is reached.
• Remove the direct-to-prod hotfix workflow so urgent production fixes use the normal staging -> production promotion path.
• Staging deployed and verified at 0.9.81-staging.74daf84b before promotion.

What's Changed

• chore(release): VERSION → 0.9.81 [skip ci] by @github-actions[bot] in #3874
• chore(dev-eks): deploy gateway dev-e444527c [skip ci] by @github-actions[bot] in #3875
• chore(dev-eks): deploy dev-e444527c [skip ci] by @github-actions[bot] in #3876
• fix(cli): push managed ship to upstream git by @markokraemer in #3877
• chore(dev-eks): deploy dev-f38b99f1 [skip ci] by @github-actions[bot] in #3878
• chore(dev-eks): deploy dev-c63e5697 [skip ci] by @github-actions[bot] in #3879
• fix(slack): answer in-thread mentions + stop dropping follow-ups during session wake by @markokraemer in #3881
• chore(dev-eks): deploy dev-9721a2b3 [skip ci] by @github-actions[bot] in #3882
• fix(web): surface sub-agent errors/retries in parent thread + sub-session modal UX by @markokraemer in #3883
• Route Zen free models natively by @markokraemer in #3885

Full Changelog: v0.9.80...v0.9.81