feat!: remove ai assistant button

[astandrik]

Summary

Removes the AI Assistant button feature from the YDB Embedded UI
interface.

Changes

• Removed AI Assistant button from the header navigation
• Cleaned up component registry by removing the AIAssistantButton
  registration
• Refactored hotkeys system to support configurable hotkey groups
  (improved extensibility)

Breaking Change

This is a breaking change as it removes a previously available UI
feature. Users who relied on the AI Assistant button will need to
use alternative methods.

Related Issue

Closes #2534

CI Results

Test Status: ⚠️ FLAKY

📊 Full Report

Total	Passed	Failed	Flaky	Skipped
354	352	0	1	1

Test Changes Summary ⏭️1

⏭️ Skipped Tests (1)

1. Scroll to row, get shareable link, navigate to URL and verify row is scrolled into view (tenant/diagnostics/tabs/queries.test.ts)

Bundle Size: ✅

Current: 84.00 MB | Main: 84.00 MB
Diff: 0.17 KB (-0.00%)

✅ Bundle size unchanged.

ℹ️ CI Information

• Test recordings for failed tests are available in the full report.
• Bundle size is measured for the entire 'dist' directory.
• 📊 indicates links to detailed reports.
• 🔺 indicates increase, 🔽 decrease, and ✅ no change in bundle size.