Add Admin runtime reasoning controls

[16francej]

Spec diff: none.

Summary

• add reasoning-level and fast-mode controls to the Admin default runtime card
• validate each option against the selected harness and model
• carry persisted defaults through runtime resolution so Slack and core turns inherit them
• preserve the controls when legacy clients update only the model

Verification

• node --experimental-test-module-mocks --test test/admin-resources.test.ts
• node --experimental-test-module-mocks --test test/runtime-selection.test.ts
• npm --prefix plugins/admin test
• npm run typecheck
• npm run lint
• live Admin save/reload in a production-shaped dev instance
• fresh Slack DM returned the requested exact response while the persisted request recorded claude-opus-5 with speed=fast
• independent adversarial review of exact commit bc73d6300 found no actionable issues

Screenshot

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