Verify encrypted backup contents before reporting success

[Jacksper13]

Summary

• require the Backup Code before verifying an encrypted backup
• share Restore's read-only decrypt and plaintext-CRC validation path with Verify
• decrypt into a single mutable plaintext buffer, clear it on failures, and explicitly zero it before Verify returns
• preserve distinct card, file I/O, malformed-header, decrypt/integrity, and out-of-memory failures
• ensure every verification and restoration error leaves the spinner flow through a terminal path
• correct archive magic validation and truncated-header error handling
• document the user-visible verification change in the changelog

The existing backup format remains unchanged. This verifies decryption and the format's plaintext CRC; it does not add cryptographic authentication.

Testing

• python -m pytest modules/tests/test_backup_reader.py modules/tests/test_verify_backup_task.py modules/tests/test_verify_backup_flow.py -q (22 passed)
• python -m pycodestyle on all changed Passport Python files
• color MicroPython simulator build
• direct MicroPython archive test covering valid decrypt, wrong code, encrypted-body corruption, malformed headers and metadata, truncation, and size limits

Dependency

This PR is stacked on #657 so the smaller callback/error-handling fix can remain independently reviewable.