fix: address PR review feedback

- ReturnTypeChanged now classified as breaking (breaks callers)
- ParamsAdded label changed to "signature changed" (can't verify defaults)
- Entity log matches file_path + entity_name to prevent cross-file misattribution
- Replace --follow (always true, no way to disable) with --no-follow flag
- Remove aggressive has_breaking_commits && dependent_count >= 5 heuristic
- compute_semver considers removed public entities with dependents as MAJOR
- Add --full flag to sem changelog and sem review to show all changes

Author: antiartificial