fix(resolution): leaf-aware subpath imports, real package.json, preset subpath shadowing

[danfry1]

Problem

Three resolution-fidelity gaps around deep (subpath) imports, all failing silently:

1. RN subpath default exports (mock engine). import Platform from 'react-native/Libraries/Utilities/Platform' — the dominant deep-import pattern in ecosystem libraries and migrated Jest suites — received the entire mock object as Platform, so Platform.OS was silently undefined. Same on the CJS side.
2. Package manifests virtualized. require('react-native/package.json').version (a common version gate) read the mock and got undefined, sending version-gated libraries down wrong code paths.
3. Preset shadowing skipped subpaths (both engines). import Swipeable from 'react-native-gesture-handler/Swipeable' bypassed the preset mock entirely and loaded the package's real native-runtime code — or failed resolution outright on package versions that no longer ship the deep file (RNGH 3.x dropped /Swipeable).

Change

• Virtual RN subpath modules (ESM) and the CJS bridge derive the intended export from the subpath's basename and serve it as the default. CJS requires get Babel-interop shape ({ __esModule, default } via a live Proxy wrapper) so both require('.../Platform').OS and _interopRequireDefault consumers work. Unknown leaves keep the previous whole-mock fallback.
• Both interception layers exempt package.json subpaths, resolving the real manifest; the mock fallback is kept when the package is not installed.
• All three preset-redirect layers (Vite plugin resolveId/load, ESM loader hook, CJS require hook) now match subpaths of preset packages, leaf-aware. Exempt: JSON subpaths, asset-extension subpaths (fonts/images keep stubbing from their real files), and Node-safe utility entries (jest-utils, jestSetup, mock, plugin), which pass through to the real file. Unknown leaves fall back to the root mock and warn under diagnostics.
• CJS interop wrappers are memoized per specifier for identity stability, keyed by the per-package mock object — not the __vitest_native_preset_mocks container, which the hot runtime reuses across files while rebuilding the per-package values. (An earlier container-keyed draft served file 1's mocks to every later file in a hot worker; caught in pre-merge review via a two-file repro.)

Tests

• tests/regression.test.ts: leaf default exports (ESM + CJS), interop shape, identity stability, real-manifest reads (ESM + CJS).
• tests/native-unit.test.ts: loader subpath redirect + JSON/asset passthrough, specifier helpers, plugin-level resolveId/load for preset subpaths, react-native/package.json carve-out, leaf-aware virtual code generation.
• tests-native/preset-subpath.test.tsx (runs under stock and hot configs): deep ESM import renders via the preset mock, root-vs-subpath identity, utility passthrough (jest-utils), real-manifest read.
• tests-native/preset-subpath-cross-file.test.tsx: cross-file twin — catches stale subpath caches in a shared hot worker as an identity mismatch. Verified in a single hot worker with --maxWorkers=1 --no-file-parallelism.

Full gate: mock suite 1291 passed, native suites (stock/hot/hot-isolation/android/navigation) green, crosscheck 75/75, packed consumer fixtures green, lint/format/typecheck clean.