Captain V2 assistants can now use every enabled custom tool from their
account through the main assistant. The change keeps existing custom
tool access when an assistant has no migrated scenarios, so switching
from V1 does not remove the capability without warning.
## How to reproduce
1. Create and enable an account custom tool.
2. Use an assistant with no custom instructions and no generated
scenarios.
3. Enable Captain V2 for the account.
4. Before this change, the main assistant receives only FAQ lookup and
handoff. After this change, it also receives the enabled account custom
tool.
## What changed
The main V2 assistant now loads enabled custom tools through its account
association. Scenario agents still load only the tools named in their
scenario instructions. The account custom tool limit keeps the added
tool count bounded.
Focused model coverage verifies enabled tools, disabled tools, account
isolation, FAQ lookup, and handoff. Existing V1 assistant, V2 scenario,
and V2 runner coverage passes. RuboCop passes.
