ci: provision mise before release and demo workflow trust #2483

Summary

Provision mise before the Base Demo E2E and ecosystem release-BOM workflows trust a selected base-demo/.mise.toml.

Problem

The current workflows run mise trust before basectl setup base-demo, but the macOS runner does not have mise installed. The latest Base Demo E2E run fails with mise: command not found before validation begins: https://github.com/basefoundry/base/actions/runs/37917926144

The setup ordering is intentional for trust safety, so the workflow needs an explicit, policy-compliant mise installation step on every platform that reaches the trust command.

Acceptance criteria

• Base Demo E2E provisions and verifies mise before the scoped trust step.
• Both Ubuntu and macOS ecosystem BOM lanes provision and verify mise before the scoped trust step.
• The trust step remains before basectl setup --ci base-demo.
• Workflow contract tests cover the ordering and missing-tool failure path.
• Hosted Base Demo E2E and a representative BOM run pass.

Release impact

This blocks the Base 1.10.0 compatibility BOM.