cli: add Nylas Agent Account support and managed send parity

[qasim-nylas]

Summary

• add nylas agent command support for create, list, delete, and status
• hardcode provider=nylas for agent account flows and verify connector readiness before create
• support --app-password during agent account creation for IMAP/SMTP mail-client access
• route provider=nylas email sends through the same managed transactional path as provider=inbox
• block unsupported managed secure-send flows instead of falling back to the wrong endpoint
• repair stale local grant state after deleting default or malformed managed grants
• update docs and add unit/integration coverage for the new behavior

Details

Agent Accounts

• adds a dedicated nylas agent command surface
• uses the nylas connector path and managed grant APIs for agent account CRUD
• handles wrapped and flat create responses correctly
• paginates managed grant listing so list/status/delete-by-email continue to work beyond the first page

App Password Support

• adds --app-password to nylas agent create
• validates password requirements locally before calling the API
• documents mail-client setup expectations for Agent Accounts

Managed Send Parity

• treats provider=nylas the same as provider=inbox for managed transactional send
• uses the grant email as the sender for managed-domain sends
• surfaces grant lookup failures instead of silently falling back to the wrong send path

Local Grant State Repair

• prevents invalid local grants with empty IDs or emails from being persisted
• repairs malformed local grant entries on read
• repairs default_grant state when a default grant is deleted or missing

Testing

• make ci-full

Jira

• Parent: TT-4304
• TT-4406 nylas agent command surface
• TT-4407 connector bootstrap and readiness checks
• TT-4408 --app-password support
• TT-4409 managed send parity for provider=nylas
• TT-4410 docs updates
• TT-4411 unit and integration coverage

[AaronDDM]

LGTM 👍