Document unified UI automation framework for test workflows and AI tooling

[Copilot]

ResInsight currently lacks a defined framework for UI-level workflow verification (e.g., create/manipulate/delete range filters) and for AI-driven UI event simulation. This PR adds a concrete, shared approach that covers both needs with one architecture.

• What was added

  • Updated docs/agents/core.md with a new UI Automation and UI Testing section.
  • Defined a single recommended stack:
    • In-app automation API: Qt Http Server (qthttpserver) exposed on localhost.
    • External runner/client: Playwright for orchestration and assertions.

• Why this architecture

  • Provides one stable automation surface for both CI-style UI workflow tests and AI tooling.
  • Avoids brittle desktop event-only automation by introducing a deterministic API boundary.

• Alternatives documented

  • QTest-only: useful for in-process widget tests, limited for external AI tooling.
  • Squish: capable but introduces commercial tooling overhead.
  • Playwright-only (no in-app API): runner is strong, but desktop Qt targeting is less robust.

## UI Automation and UI Testing

- Automation transport: Qt Http Server (`qthttpserver`)
- Automation client/test runner: Playwright