fix: make Ukrainian the built-in translation language

[xand0dev]

Summary

• change the built-in translator route from English ↔ Russian to English ↔ Ukrainian
• add regression coverage for both translation directions
• rerecord the README walkthrough so the live Translate pane shows АНГЛІЙСЬКА → УКРАЇНСЬКА
• replace transition-sensitive captions with one stable product-tour legend

Root cause

The translator service had ru hardcoded as its non-English language, and the previous walkthrough faithfully exposed that product behavior. The original visual QA checked the animation flow but failed to review the language choice as release content.

Impact

VoidBar now uses Ukrainian as its built-in translation language and the public README demo matches the actual product behavior.

Validation

• swift test — 7 tests passed, including two new translator route tests
• release app bundle built successfully
• inspected a full 2 fps contact sheet of the final 8.4-second recording
• verified the Translate frames show АНГЛІЙСЬКА and УКРАЇНСЬКА
• verified the GIF as 1068×450 and 584 KB
• git diff main...HEAD --check