🔐 Add keystore management scripts and documentation [skip ci]

- Add create-keystore.fish: Generate new release keystore with auto-generated passwords
- Add verify-secrets.fish: Verify GitHub Secrets and local keystore setup
- Add build-release-local.fish: Build signed release APKs locally
- Add LOCAL_BUILDS.md: Documentation for local release builds
- Add key.properties.example: Template for signing configuration
- Update android/.gitignore: Protect sensitive keystore files
- Integrate GitHub CLI for automatic secret management
- All scripts support both manual and automated workflows

android/.gitignore

@@ -13,3 +13,8 @@
 .externalNativeBuild
 .cxx
 local.properties
+
+# Signing configuration (contains sensitive keys)
+key.properties
+*.jks
+*.keystore