feat(uec): UEC-first architecture with strict adapter contract enforcement

[m2papierz]

Summary

This PR implements the "UEC-first" architecture where ExecutionEnvelope becomes the single source of truth for program and result data. Key changes:

• Schema extension: Added parametric_hash and executed_parametric_hash to ProgramSnapshot for distinguishing structural vs parametric changes (VQE support)
• Strict contract enforcement: Adapter runs without envelope now raise MissingEnvelopeError (strict mode). Engine no longer silently synthesizes envelopes for adapter runs.
• Bit order canonicalization: Single canonicalize_bitstrings() function in engine handles all bitstring normalization to cbit0_right format before comparison.
• Manual runs: Continue to work with auto-generated envelopes but with documented limitations (no program hashes, compare reports "HASH_UNAVAILABLE").
• Program comparison: New ProgramMatchStatus enum with FULL_MATCH, STRUCTURAL_MATCH_PARAM_MISMATCH, STRUCTURAL_MISMATCH, HASH_UNAVAILABLE for precise diff reporting.

Type of change

• Bug fix
• New feature
• Refactor (no user-facing change)
• Docs only
• CI/build tooling
• Breaking change

Changelog (user-facing only)

• I added a towncrier fragment in changelog.d/ (skip for internal-only changes)

Checklist

• I ran lint locally (uv run pre-commit run --all-files)
• I ran tests locally (uv run pytest)
• I added/updated tests for behavior changes
• I updated docs/README/examples if needed
• If I changed dependencies, I updated uv.lock (uv lock) and committed it
• I considered backward compatibility and security impact

Notes for reviewers

Notes for reviewers

• Breaking change for adapters: All adapters need to be updated to provide program_hash and parametric_hash. During migration, use strict=False in resolve_envelope().
• Backward compatibility: diff_runs() uses strict=False internally so existing runs still work. Warnings are logged for adapter runs missing envelopes.
• Manual runs: Work as before, but compare now clearly reports HASH_UNAVAILABLE instead of silently skipping hash comparison.

Follow-up work:

• Update all adapters to provide program hashes
• Add tests for canonicalize_bitstrings() with multi-register format
• Consider adding strict=True enforcement in CI after adapter migration