Add property-based tests for import-boundary layer-pair matrix (fast-check)

[coderabbitai]

Background

PR #3 introduced architectural boundary invariants enforced by scripts/import-boundaries.ts over a 5×5 layer-pair matrix (domain, application, adapters, app, other). The current test suite uses only example-based cases and does not exhaustively verify all 25 import-direction combinations.

Requested work

Add property-based tests using fast-check to tests/import-boundaries.test.ts (or a new tests/import-boundaries.property.test.ts) that:

1. Generate arbitrary source-file pairs (sourceLayer, targetLayer) drawn from the full 5×5 matrix.
2. Assert that findBoundaryViolations emits a violation if and only if the pair is in the forbidden set.
3. Cover all 25 combinations, including self-imports (e.g. domain → domain).

Provide rigorous reasoning or a proof sketch if any range-sensitive invariant makes exhaustive property testing unnecessary.

Acceptance criteria

• bun test passes including the new property-based tests.
• All 25 layer-pair combinations are covered.
• No dependency on example fixtures for coverage of the boundary rule logic.

References

• PR: Record source-tree boundary decision (1.1.2) #3
• Requester: @leynos