feat: rebuild review pipeline with backends, suppressions, and SARIF

[akosidencio]

Description

Summary of the changes and the problem they solve.

Closes # (issue)

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactoring / cleanup

Requirements addressed

• Implements / closes:

Testing

• cargo test --workspace passes
• cargo clippy --all-targets -- -D warnings passes
• cargo fmt --check passes
• Manual CLI test: diffmind --branch main runs without error
• Manual CLI test: diffmind --stdin --format json produces valid JSON

Checklist

• Code compiles with zero warnings (cargo build)
• Logic is covered by a unit test where feasible
• Public API or CLI flags documented in README if changed
• REQUIREMENTS.md acceptance criteria checked off if applicable