Amend configuration ADRs for the two-module subsystem

## What to build

Bring the accepted configuration records back into agreement with the architecture that the code and fitness functions currently enforce: a small public configuration interface over a private configuration foundation, with both modules constrained to dependency-free package leaves and the standard library.

Treat this as an additive, behavior-neutral amendment under ADR 0000, not a new or superseding decision. The layered-configuration record should own the complete dependency rule; later profile records and adjacent contributor prose should cite it rather than restating a stale single-module model.

## Acceptance criteria

- [ ] No current configuration ADR claims that configuration is a single module or that exceptions are its only first-party dependency.
- [ ] The owning record states the permitted dependencies for both the public interface and private foundation exactly as the fitness function enforces them.
- [ ] The owning record's status and notes identify the additive amendment and explain that public imports and behavior did not change.
- [ ] Later configuration records cite the owning dependency rule instead of duplicating it.
- [ ] Adjacent contributor and architecture prose contains no stale single-module description.
- [ ] No production code, public import path, configuration behavior, or fitness-function policy changes.
- [ ] ADR-reference checks, architecture tests, dependency contracts, and the documentation build pass.

## Blocked by

None — can start immediately.