fix(amicus): silent fallback for AmicusFab ErrorBoundary + provider-tree smoke test

[CraigBuckmaster]

Summary

Follow-up polish to #1557. The architectural move (<AmicusFab /> inside <NavigationContainer>) and the defensive try/catch in AmicusFab.tsx both landed in #1557. This PR adds two pieces that were outlined in the original plan but deferred:

1. Silent fallback for the AmicusFab ErrorBoundary

The default ErrorBoundary fallback is a flex: 1 centered "Something went wrong" view with a Retry button. If the FAB ever errors during render — say, a future regression puts it outside NavigationContainer again — that full-screen fallback would displace real UI. A FAB failure should be invisible to the user. Telemetry still captures it via logger.error in componentDidCatch.

• ErrorBoundary.tsx — extend Props with an optional renderFallback render-prop. When provided, it is used instead of the default centered fallback. Default behavior and all existing call sites unchanged.
• AmicusFabErrorFallback.tsx — new component that renders null.
• App.tsx — the AmicusFab ErrorBoundary now uses renderFallback={AmicusFabErrorFallback} in place of fallbackMessage.

2. Provider-tree smoke test

app/__tests__/App.providerTree.test.tsx — mounts <App /> with the real @react-navigation/native (not the non-throwing jest.setup.js stub), waits for dbStatus -> 'ready', and asserts the full tree composes without throwing. This is the test that would have caught #1557's root cause before it reached TestFlight.

Heavy / native-bound / out-of-scope dependencies (RootNavigator, stores, DB init, Sentry, the notification router, the crash handler) are mocked. The NavigationContainer composition itself runs for real — that's the point.

Validation

• npx tsc --noEmit — clean
• npm run lint — clean
• npm test — 466 suites, 3433 tests pass (1 new smoke test, no regressions)
• Targeted: npx jest --testPathPattern "AmicusFab" — 9 tests pass
• Targeted: npx jest --testPathPattern "App.providerTree" — 1 test passes

What this PR does NOT do

• No changes to AmicusFab.tsx — the defensive try/catch from fix(amicus): prevent AmicusFab crash when mounted outside NavigationContainer #1557 stays as belt-and-suspenders regression prevention.
• No changes to AmicusPeekSheet.tsx — its useNavigationState call now succeeds naturally because AmicusFab (and therefore the sheet, rendered as its child) is inside NavigationContainer.
• No changes to Sentry, OTA, DB, or navigation internals.
• No new runtime dependencies.

Follow-ups that remain open

1. Audit other components for unguarded useNavigation() / useNavigationState() / useRoute() calls.
2. Document the "hook must be inside its required provider" rule in DEV_GUIDE.md with a code-review checklist item.

[github-actions]

Test Results

✅ All tests passed

	Passed	Failed	Total
Tests	✅ 3433	❌ 0	3433
Suites	✅ 466	❌ 0	466

Coverage

Statements	Branches	Functions	Lines
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⏱️ Duration: 86.3s