[Android] Add Russian (ru) localization #94

Android feature request

Add Russian (ru) as a built-in language to the Android version of Aether. The implementation in the companion pull request adds Russian Compose resources under values-ru/, registers the locale in the Android language selector, and translates the Android shared interface and extension settings.

Included

• Russian strings.xml, shared_extensions.xml, and shared_conversation_messages.xml;
• Android language selector registration;
• Russian labels for Web Access, MCP Servers, Subagents and nested settings.

The translation is based on Aether v2.1.6 Android resources and preserves placeholders.