fix: address PR37 review feedback — zero line counts and verification enum YAML

[haasonsaas]

Summary

• diff_parser: Add regression assertions and a TDD test for zero line counts in hunk headers (@@ -0,0 +1,N @@ and @@ -N,N +0,0 @@). PR37/Bugbot had flagged that a .filter(|v| *v > 0) would break new/deleted file parsing; main already uses parse_optional_capture without that filter; these tests would fail if it were re-introduced.
• config: Add tests that deserialize verification_model_role and verification_consensus_mode from YAML (flat keys into config.verification). Covers weak/majority and primary/all; uses config.verification.model_role / consensus_mode after the VerificationConfig flatten refactor on main.

Test plan

• cargo test diff_parser — 15 tests (includes test_parse_deleted_file, test_parse_new_file, test_parse_new_file_multi_line_zero_old_lines).
• cargo test test_config_deserialize_verification — 2 tests for YAML deserialize of verification enums.
• CI: version, lint, security, test, mutation, review.

Made with Cursor

[cursor]

PR Summary

Low Risk
Test-only changes that add regression coverage for diff parsing edge cases and YAML config deserialization; no production logic changes.

Overview
Adds regression/TDD tests to ensure DiffParser preserves old_lines/new_lines when hunk headers contain zeros (new/deleted files), including multi-line additions.

Adds YAML deserialization tests to verify flattened verification_model_role and verification_consensus_mode enum fields correctly populate config.verification (e.g., weak/majority, primary/all).

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