Shrink release APK 68% and fix broken release bundling

[dfalling]

Summary

Three small config changes (no product code), measured with real assembleRelease builds.

Fixes a broken release build. The release JS bundle could not build at all: graphql v17 ships .mjs using export * as Kind from ... (export-namespace-from), which the RN Babel preset doesn't transform. CI only runs assembleDebug — Metro serves JS live and skips bundling — so it never surfaced, but any v* release tag would have failed. Adding @babel/plugin-transform-export-namespace-from (already a transitive dep) fixes it.

Shrinks the shipped APK ~68%: 110 MB → 35 MB.

Build	APK size	Build time
All 4 ABIs (previous)	110 MB	~4 min
arm64-v8a only	39 MB	~35 s
arm64-v8a + R8 + resource shrink	35 MB	~19 s

• arm64-v8a only — the dominant lever (110 → 39 MB). x86/x86_64 are emulator-only and armeabi-v7a is pre-2017 32-bit; GrapheneOS/Pixels and modern stock Android are all 64-bit ARM. Also ~4× faster builds. Debug on x86_64 emulators still works via -PreactNativeArchitectures=x86_64.
• R8 + resource shrinking — smaller lever (39 → 35 MB; shrinks dex 17.5 → 5.6 MB).

Notes / risk

• R8 warrants one on-device smoke test before the first release — minification can strip reflection-accessed code in native modules. Net benefit here is only ~4 MB; if you'd rather play it safe, set enableProguardInReleaseBuilds = false and you're still at 39 MB.
• Verified: tsc, biome, jest all pass; release APK builds and is structurally correct (single ABI, all expected libs + bundle present). Not runtime-verified — no arm64 device/emulator available in this environment.