feat(ui): move dark theme toggle into view options menu (#903)

[DashratRajpurohit]

Summary

Resolves Part 1 of #903 (Clean up Phoenix bar): Moves the Dark Theme toggle directly into the View Options menu (ViewOptionsComponent) and removes the standalone dark theme button from the primary bottom menu bar to reduce interface clutter.

Visual Changes & Screenshots

Light Theme & Clean Toolbar

Dark Theme Active on ATLAS Detector

Highlights:

1. Decluttered Bottom Toolbar: Removed standalone <app-dark-theme> button from ui-menu.component.html, opening up toolbar space.
2. View Options Integration: Added [✓] Dark Theme Material checkbox directly inside the View Options dropdown menu (view-options.component.html).
3. Instant Toggle: Toggling Dark Theme inside View Options seamlessly updates UIManager dark mode state across 3D detector viewports.

Changes Made

• ViewOptionsComponent:
  • Added darkTheme state property initialized from UIManager.getDarkTheme().
  • Added setDarkTheme(change: MatCheckboxChange) handler to toggle dark theme.
  • Added Dark Theme checkbox menu item to view-options.component.html.
  • Added unit test suite in view-options.component.test.ts.
• ui-menu.component.html:
  • Removed standalone <app-dark-theme> component tag from the main bottom menu wrapper.

Test Plan

• Unit tests added and passing in view-options.component.test.ts.
• Verified locally on http://localhost:4200/ and http://localhost:4200/atlas.