Transcrape v0.2.0

Fix the two release-CI failures

Android: GitHub Actions strips the trailing newline off secrets, so the
restored keystore.properties glued storeFile onto the password line and
gradle died on a null cast at configuration time. The signing script now
guarantees a newline before appending.

macOS: whisper.cpp's ggml uses std::filesystem, which needs macOS 10.15;
Tauri's default deployment target is 10.13, so a fresh CI build failed where
local builds had a cache to lean on. Pin minimumSystemVersion to 10.15.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>