Captain auto-resolve policy is now owned by each assistant. Existing
assistants first read an assistant-level setting, fall back to the
current account setting during rollout, and are backfilled
asynchronously so behavior is preserved.
## Closes
[AI-163](https://linear.app/chatwoot/issue/AI-163)
## How to test
1. Configure different auto-resolve modes on two assistants in the same
account through the API.
2. Confirm each assistant follows its own mode when the inactivity job
runs.
3. Confirm an assistant without the new setting follows the existing
account mode.
4. Run the migration job and confirm the account mode is copied without
overwriting an existing assistant mode.
5. Confirm evaluated mode falls back to time-based resolution when the
`captain_tasks` capability is unavailable.
## What changed
- Added assistant-level `disabled`, `legacy`, and `evaluated` policy
storage and validation.
- Updated scheduling and resolution runtime reads to use the assistant
policy.
- Added a compatibility fallback and asynchronous backfill from the
account setting.
- Preserved the account-level `captain_tasks` capability gate for
evaluation.
- Kept this foundation independent of the Captain V2 guard; the timer
and advanced settings in stacks 2–5 are Captain V2-only.
Stack 1 of 5. This is the base for #15303.
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