fix(iOS): avoid lazy tab flash on iOS 27

[thiagobrez]

Fixes #547.

PR Description

iOS 27's shouldSelectTab delegate switches the native TabView immediately. On a lazy route's first activation, React had not mounted that scene yet; TabView also rendered its empty placeholder for the newly focused route's first render. The native transition therefore exposed an empty white content frame.

This PR sends each route's internal loaded state to iOS. On iOS 27 only, native selection of an as-yet-unloaded lazy tab is declined for that event, leaving the current scene visible while the existing controlled selection callback runs. The newly focused route is materialized in that same React render, and the subsequent controlled update selects it. Already-loaded and eager tabs retain immediate native selection.

This is deliberately scoped to iOS 27's delegate path: iOS 26 and earlier keep their existing selection behavior, Android ignores the internal field, custom content backgrounds remain visible, and default lazy semantics are preserved. There are no delays, eager rendering, masks, or public API changes. A patch changeset is included.

How to test?

Automated/local validation:

• yarn build — passed
• yarn lint — passed (two existing React Native deep-import warnings)
• yarn typecheck — passed
• focused isRouteLoaded Jest regression suite — 3 passed
• yarn build:android — passed
• iOS 27 Debug simulator xcodebuild — passed
• aggregate yarn test — existing repository runner stops because @bottom-tabs/react-navigation contains no tests; the new focused suite passes independently

Device verification used agent-device 0.20.10 with Xcode 27.0 (27A5228h), React Native 0.81.4/Hermes/New Architecture, and an iPhone 17 Pro simulator:

1. Reproduced before the change on iOS 27.0 runtime 24A5390f with the example app's default-lazy Native > Lazy Tabs flow.
2. Recorded the first Contacts activation at 50 fps; the sampled frames contain a fully white content frame.
3. Rebuilt after the fix and repeated the exact activation at 75 fps; Article remains visible until Contacts is mounted, with no empty frame.
4. Repeated with a lazy screen whose permanent background is #1E2D2F; no white or empty frame appears.
5. Repeated the first-load Contacts path on an iOS 26.5 simulator (23F77); the scene loads normally.

The complete environment, steps, explicit accessibility assertions, logs, and artifact index are in artifacts/issue-547/README.md.

Screenshots and videos

Before:

• Three-second reproduction video
• Transition contact sheet
• Captured white frame

After:

• Default first-load video
• Default transition contact sheet
• Dark-background first-load video
• Dark transition contact sheet
• iOS 26.5 compatibility screenshot
• iOS 27 build log

Required CI status: all nine CI and CodeQL checks passed, including lint, SwiftLint, library, Android, and iOS builds.