feat: implement JSON Schema for commitizen config (issue #1565)

- Add scripts/gen_json_schema.py: generates schema from Settings/CzSettings TypedDicts
- Add tests/test_json_schema.py: 18 tests validating schema generation, type mapping, defaults, and validation
- Add schemas/commitizen-config.schema.json: committed schema (schemastore.org-compatible)
- Update pyproject.toml: add jsonschema dependency to test group

The schema covers all config keys under [tool.commitizen] including nested customize.
All tests pass, ruff clean.

Author: FreakyAdy

pyproject.toml

@@ -108,6 +108,7 @@ test = [
     "pytest-xdist>=3.1.0",
     "pytest-gitconfig>=0.9.0",
     "pre-commit>=4.5.1",
+    "jsonschema>=4.26.0",
 ]
 
 linters = [