Establish Australian requirements and dual-database CI baseline

[ChilliGeologist]

Scope

First Phase 0 change in the Australian fork. No application, tax-calculation or payroll behaviour changes.

• Document the existing jurisdiction boundaries and follow-up audit targets.
• Add 21 initial Australian requirements with separate research/delivery status.
• Record actual baseline evidence and unresolved source/runtime checks.
• Include australia in tests/lint/security triggers.
• Run tests on SQLite and disposable MySQL 8.4, with npm ci.

Validation

• Existing JavaScript tests: 60 passed, zero failures (local Node 24.19.0).
• git diff --check passed.
• PHP/Pest, Pint, PHPStan, asset build and audits await CI; PHP/Composer/MySQL/Docker are not available locally.
• Not a compliance claim. No live data, deployment or tax submission.

Review is within this fork only, not an upstream contribution.