Unit tests for Python report renderers (report.py)

[ToryMic]

Goal

The Python report renderers (schemalock/report.py: render_console, render_json, exit_code) are untested — there is no tests/test_report.py. Add tests mirroring the Rust-side report tests so both languages' output contracts are locked.

Scope

• Create tests/test_report.py.
• Cover render_console with mixed Pass/Fail/Error CheckResults (assert per-check lines and the summary line).
• Cover render_json: assert the written file is valid JSON with the exact config_name/summary/results shape, including error outcomes.
• Cover exit_code for all-pass (0) vs any-non-pass (1).
• Follow existing test conventions (see tests/test_config.py and tests/test_checks.py for fixture style).

Why

Python's JSON report is diffed byte-for-byte against Rust in the CI parity gate (scripts/parity_check.py). Locking both sides' renderers prevents drift between the ports.

Success criteria

• pytest passes with the new file under ruff check . and ruff format --check . clean.
• Every public function in schemalock/report.py is exercised at least once.