fix(mobile): match react version to react-native 0.85.3 vendored renderer (19.2.3)

[KrzysztofMoch]

Problem

pingdotgg#4643 (commit 108e01746) bumped react/react-dom from 19.2.3 to 19.2.6 in apps/mobile. react-native@0.85.3 vendors a renderer built against react 19.2.3, and the legacy (Paper) renderer performs a module-scope exact-version check against React.version (ReactNativeRenderer-prod.js, ~line 10922). This app evaluates the Paper renderer during initial bundle evaluation (via the lazy RendererProxy bindings), so every fresh native build crashes at startup (signal 6), before the splash screen resolves:

*** Terminating app due to uncaught exception 'RCTFatalException: Unhandled JS
Exception: [runtime not ready]: Error: Incompatible React versions: The "react" and
"react-native-renderer" packages must have the exact same version. Instead got:
  - react:                  19.2.6
  - react-native-renderer:  19.2.3

This also affects any OTA bundle built from current main — the fingerprint runtime policy won't save existing binaries from a JS-only mismatch, so an OTA push would crash already-shipped apps.

Fix

Revert react and react-dom to 19.2.3 in apps/mobile/package.json (exact pre-pingdotgg#4643 versions) and update pnpm-lock.yaml. No react-native 0.85.x patch release with a 19.2.6 renderer exists (0.85.3 is the latest), so pinning react back is the only correct fix. Patching the renderer version string is not an option — the exact-match check exists because ReactSharedInternals may differ between patch releases.

apps/web intentionally stays on react 19.2.6 (the workspace resolves react per app; the lockfile still resolves 19.2.6 there).

Verification

• react resolved from apps/mobile is 19.2.3, matching the only version string in the vendored ReactNativeRenderer-prod.js.
• Mobile tsc --noEmit and repo lint pass with no new issues.
• Built APP_VARIANT=production + Release for the iOS simulator, launched it: app gets past startup and renders the Threads screen; no Incompatible React versions exception in simulator logs.

Note (pre-existing, unrelated): a plain expo run:ios --configuration Release targeting a simulator fails because the vendored GhosttyKit.xcframework simulator slice is arm64-only while Release builds all archs (arm64 x86_64); verification used ONLY_ACTIVE_ARCH=YES. Device/EAS Release and Debug simulator builds are unaffected.

[KrzysztofMoch]

Closing — opened without explicit request.