Improve Typesense local workflow and bot resilience

[ThaddeusJiang]

Summary

• align local Typesense setup to port 8108 and add typelens in compose
• add Typesense migration/reset tasks and document local migration flow
• make bot Typesense operations fault-tolerant to avoid flow interruption on indexing/search failure
• update Cobalt error handling to return error tuple instead of raising
• add agent guidance and a Zeabur env mismatch postmortem

Commits

1. chore(typesense): align local setup and add migration utilities
2. feat(bot): degrade gracefully when typesense calls fail
3. refactor(cobalt): return error tuple instead of raising
4. docs: add agent guide and zeabur env postmortem

Validation

• git status is clean
• Changes are split by concern into 4 commits