feat: add --require-license strict mode flag

[Coding-Dev-Tools]

Feature Request

After merging ix/optional-license-dep, the
evenueholdings-license dependency is now optional. The CLI gracefully degrades with a no-op stub when the package is not installed.

Request: Add a --require-license flag (or REVENUEHOLDINGS_REQUIRE_LICENSE=1 env var) that enables strict mode - when set, the CLI raises an error instead of silently skipping license checks.

Use Cases

• Production deployments where license enforcement is mandatory
• CI/CD pipelines that need to verify license compliance
• Debugging license-related issues in development

Acceptance Criteria

• --require-license flag added to main CLI group
• REVENUEHOLDINGS_REQUIRE_LICENSE env var supported
• When set and package not installed: exit with clear error
• When set and license check fails: propagate the error
• Documented in README