feat(ui): add subtle sponsor link

[papi-ux]

What changed

• adds a compact ♥ Sponsor action beneath Help and About in Nova's System drawer
• routes it through the existing browser and in-app WebView launcher to https://github.com/sponsors/papi-ux
• keeps the control controller-focusable and gives it a descriptive accessibility label
• pins the exact destination, callback wiring, compact presentation, and Java-compatible launcher API in tests

Why

GitHub Sponsors should be discoverable in Nova without becoming a primary navigation action or competing with host controls.

User impact

Users can open the papi-ux GitHub Sponsors page from a quiet footer action in System. Existing Help, About, host, and streaming controls are unchanged.

Validation

• RED: both new sponsor contracts failed before implementation
• GREEN: 10 focused launcher, API, and System drawer tests
• GREEN: Android lint with lintFailOnError=true
• GREEN: public surface and public docs checks
• GREEN: git diff --check
• full local unit run reached 1,306 tests with all affected tests passing; 7 unrelated failures remained: 3 existing artwork-cache eviction assertions and 4 Android 36 Robolectric classes that require Java 21 while the local runner has Java 17

No streaming, pairing, or host-management behavior changes.