Add release signing configuration and keystore.

The `build.gradle.kts` file is updated to include a release signing configuration that uses environment variables for passwords and references a new `keystore.jks` file. Minification is enabled for release builds.

🔧 fix(Sogou.kt): correct URL path in download function for Sogou dict…

…ionary import

Remove duplicate addition of Locale.SIMPLIFIED_CHINESE in LanguageFra…

…gment.

Update version name to "1.0.6"

Update version name to "1.0.5"

Add design guidelines and improve installation instructions in README.

Update application theme to use dynamic colors for night mode.

Update default frequency and appid values in EditWordFragment.

Add release signing configuration to build.gradle.kts file.