chore(mobile): upgrade @testing-library/react-native to v14 (needs React 19.2)

[ankit-yc]

Summary

Upgrade @testing-library/react-native from 13.x to 14.x in apps/mobileAppYC. This is blocked on a React version bump, so it was held back out of the jest 30 chore PR (#1959) rather than landed with it.

Problem / motivation

Dependabot offered v14 inside the grouped testing bump. Taking it made 283 of 456 mobile suites fail.

Two independent blockers:

1. React version. v14 replaces react-test-renderer with the new test-renderer package, whose react-reconciler requires React 19.2. react-native 0.81 pins React 19.1, so render() returns an unusable object.
2. Removed queries. v14 drops the UNSAFE_* queries, which these suites currently use.

Holding at ^13.3.3 keeps the other three testing-group bumps (jest 30 and friends) shippable. The cost is that apps/mobileAppYC stays a major behind on its testing library, and dependabot will keep re-offering v14.

Proposed solution

1. Move react-native to a version that pins React >= 19.2 (or otherwise get React 19.2 into the mobile workspace without breaking RN).
2. Add test-renderer and drop react-test-renderer plus @types/react-test-renderer.
3. Migrate every UNSAFE_* query to a supported query.
4. Bump @testing-library/react-native to 14.x and get all mobile suites green.

Scope

• apps/mobileAppYC/package.json (@testing-library/react-native, react-test-renderer -> test-renderer, React/RN versions)
• Mobile test files using UNSAFE_* queries
• Any test importing react-test-renderer directly - there are currently 17 such files

Out of scope

• Product behaviour in the mobile app
• The jest 30 migration itself, which lands in chore(repo): bump the testing group across 1 directory with 4 updates #1959

Current state / where it plugs in

apps/mobileAppYC is on @testing-library/react-native ^13.3.3, react-test-renderer 19.1.0, react-native 0.81.4, React 19.1.0.

Note this overlaps the mobile test-teardown work: 17 files drive react-test-renderer directly, which is the same surface as #1822 and PR #1821. Sequencing matters - doing this before or after that work, not concurrently.

Acceptance criteria

• @testing-library/react-native on 14.x
• test-renderer replaces react-test-renderer, and @types/react-test-renderer is gone
• No UNSAFE_* queries remain in mobile tests
• All mobile suites pass (456 suites / 7400 tests as of the jest 30 work)
• React Doctor stays at or above the 95 CI gate

Test plan

Full apps/mobileAppYC Jest suite with TZ=UTC, plus type-check and lint. Run the full suite several times consecutively - this workspace has a known cross-suite flake profile, so a single green run is not sufficient evidence.

Alternatives considered

• Take v14 now and pin React 19.2 directly. Rejected: it would put the React version out of step with what react-native 0.81 expects.
• Ignore the major in dependabot config. Hides the work rather than tracking it, and the PR would stop being re-offered.

Dependencies & risks

• Gated on a react-native / React upgrade, which is a much larger change than the testing library itself.
• Touches the same files as test(mobile): fix react-test-renderer teardown leaks flaking the CI suite #1821 / Flaky mobileAppYC Jest suite: one random test fails per full parallel run #1822, so coordinate sequencing.
• Migrating away from UNSAFE_* queries can change what the tests actually assert - each migration needs review, not a blanket find-and-replace.

Additional context

Held back in #1959. Failure signature on the attempted upgrade: render returning an unusable object across 283 of 456 suites.