refactor: establish capability pack architecture foundation

[MarcoPorcellato]

Summary

• freeze a hash-manifested compatibility baseline for CLI, plan, receipt, policy, verification, dry-run, and public Rust API behavior;
• introduce a private run dependency seam while preserving the existing public facade and observable contracts;
• add the approved Clean Architecture and Capability Packs specification plus the detailed TDD plan for the inert M2 library contract;
• preserve a durable programme checkpoint and restart handoff.

Validation

Recorded local evidence for the M1 code head includes:

• cargo fmt --check;
• strict Clippy with warnings denied;
• compatibility, plan CLI, receipt, matrix, and verification contract suites;
• full host suite: 467 passed, 5 ignored across 27 suites;
• downstream public-facade compile fixture;
• independent specification and code-quality reviews with no unresolved findings.

Commits after the M1 closure contain documentation and planning only. Hosted Rust CI on this exact PR head remains required before M2 implementation begins.

Boundaries

• no Capability Pack production implementation or official pack exists yet;
• no CLI, receipt, policy, configuration schema, matrix, or verification contract is intentionally changed;
• no release, stable installation, tag, or package publication is included;
• CCP heavy work is not used for this public-repository integration gate.

Next gate

Keep this PR in draft until hosted Rust CI succeeds on exact head a1bae40c4536c3b4051e712b267dd8a28c06d87f. M2 Task 1 starts only after that exact-head result is reviewed.