chore(rfl-128): add contracts/ mini-workspace (prep for move)

[kpernyer]

Summary

• Adds contracts/Cargo.toml — a minimal standalone workspace (one member: helm-module-contracts)
• Adds contracts/crates/helm-module-contracts/ — same source and manifest as crates/helm-module-contracts/

Why this is a separate PR

The main move PR (#10) removes crates/helm-module-contracts/ and updates all internal path deps. But the helms CI loads atelier-showcase main via the organism-domain workspace patch, and atelier-showcase main still references the old crates/ location. This creates a deadlock:

• Helms PR feat(helm-module-contracts): extract HelmModule + ModuleState from runway-app-host (RFL-128) #10 CI fails because atelier main has the old path (not yet merged)
• Atelier PR fix(deps): patch crates-io so shared converge/organism crates resolve from sibling paths #9 CI fails because helms main doesn't have contracts/ yet

This prep PR breaks the deadlock:

1. Merge this PR → helms main has contracts/ available (old crates/ path still intact)
2. Atelier/arena-tests PR CIs can now resolve the new path → merge those PRs
3. Helms PR feat(helm-module-contracts): extract HelmModule + ModuleState from runway-app-host (RFL-128) #10 CI can now load atelier's updated main → passes → merge

Merge order: this prep PR → atelier-showcase #9, arena-tests #7 → helms #10 → runtime-runway #15 → reflective #16

Fixes: https://linear.app/reflective/issue/RFL-128

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Note

Low Risk
Additive layout and duplicated crate source only; no dependency rewires or removals in this PR.

Overview
Adds a standalone contracts/ Cargo workspace so helm-module-contracts can be path-dep’d from other repos (e.g. runtime-runway) without pulling in the full helms workspace.

The workspace root is contracts/Cargo.toml with a single member, contracts/crates/helm-module-contracts/, mirroring the existing crate (readiness types, HelmModule / ModuleState mounting contract, and unit tests). The old crates/helm-module-contracts location is unchanged in this PR—this is prep for a later move and cross-repo path updates (RFL-128).

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[kpernyer]

Superseded by #10 (same contracts/ move, #10 included the full fix and merged).