20260629

Build armeabi-v7a (32-bit ARM) for Python 3.13/3.14 (#25)

CPython's official Android/android.py lists arm-linux-androideabi in its
supported HOSTS for both 3.13 and 3.14, and beeware's cpython-android-source-deps
publishes the matching 32-bit dependency tarballs. PEP 738 makes 64-bit Android
the *tested* Tier-3 configuration; it does not prevent building 32-bit ARM. So
the only blocker was a self-imposed ABI gate in build.sh.

- build.sh: allow armeabi-v7a through the 3.13+ official-build ABI case.
- build-all.sh: read android_abis from manifest.json (same source the CI
  packaging step uses) instead of a separate hardcoded version gate, so the
  build set and package set stay in lockstep.
- manifest.json: add armeabi-v7a to 3.13 and 3.14.
- README/android/README: correct the "3.13+ are 64-bit-only" note.

Validated locally: 3.14.6 and 3.13.14 both build via android.py and package
into Dart tarballs; libpython and extension modules are ELF32/ARM with no
import failures.