Use custom OAuth profile for Claude model catalogs

[JJ27]

What changed, and why?

Isaac authenticates through a custom OAuth CLI profile. Claude's model-picker lookup instead used the ordinary workspace profile, so a valid Isaac login still failed at launch if the ordinary profile had no cached credentials. Use the profile established by custom OAuth setup for both Claude catalog lookups.

Validation

• Reproduced the launch failure with USE_DBEXEC=0 isaac on UG ca0804b.
• Regression cases for default, model-location, and provider catalogs fail before the fix and pass afterward; ordinary authentication is covered with custom OAuth disabled.
• tests/test_cli.py, tests/test_custom_oauth.py, and tests/test_integration_contract.py: 692 passed.
• Ruff check/format and ty check passed.
• Live fixed-wheel check: USE_DBEXEC=0 isaac with SMART_ROUTER_CONFIG_VERSION=subagent_only_v1 and no explicit model completed a native subagent task. The router selected claude-haiku-5-5; the child transcript and Claude model-usage output confirm that model ran and returned the correct answer. Tested with Claude Code 2.1.299.