Add AppleSiliconAdapterEvidence normalization design and fixtures

[mdheller]

Replacement non-draft PR for the completed Copilot branch from #16 / issue #15, created because the original PR remained stuck in draft/action_required and the connector ready-for-review mutation is broken.

Scope:

• add AppleSiliconAdapterEvidence normalization design doc;
• add raw Apple Silicon dry-run evidence fixture;
• add normalized BootEvidence dry-run fixture;
• update Makefile fixture validation;
• update repo maturity metadata.

Validation evidence from Copilot branch:

• make validate passes locally across all fixture paths.
• python -m pytest passes, 8/8 tests.

Boundaries:

• no Secure Enclave calls;
• no boot-entry mutation;
• no disk writes;
• no installer execution;
• no rollback execution;
• no runtime behavior change.

Closes #15.