[TASK][CORE-01.T01] Bootstrap the Rust workspace and architectural checks

Parent: #2

Task ID: `CORE-01.T01`

## Proposed implementation
Create the Cargo workspace, pinned toolchain, formatting/lint configuration and minimal contracts/ipc/fixture-worker packages. Add a dependency-direction check so domain contracts cannot import GUI, CEF, OS brokers or provider SDKs.

## Done when
A clean checkout builds on the initial CI host and a deliberately forbidden dependency makes the architecture check fail.

## Guardrail
Keep optional engine/model builds outside default CI until artifacts/licenses are pinned; do not create empty crates for future concepts.

## Prerequisites
None

Review: pending · Implementation: not started.

Start by defining the Cargo workspace, pinned toolchain, formatting and lint configuration, then add the contracts, ipc, and fixture-worker packages described in the task. Verify a clean checkout builds on the initial CI host and that a deliberately forbidden dependency causes the architecture check to fail; keep optional engine/model builds outside default CI.

Written by the indexing model from the issue text.