Feature/UI control panel

[rajkandula]

Description

This PR introduces a floating, glassmorphic Control Panel UI to the GaussianSplats3D viewer. It allows developers and users to adjust rendering variables in real-time, view rendering stats, and reset settings easily.

Features Added

• Visual Controls: Sliders to adjust Splat Scale and Focal Length.
• View Modes & Debug: Checkbox toggles for Point Cloud mode, Orthographic Camera, Mesh Cursor, and Control Plane.
• Performance Readouts: Real-time FPS and Last Sort Time display.
• State Synchronization: Updates the UI dynamically if variables are changed via keyboard shortcuts (like = or -).
• Collapsible Layout: Click the header to collapse the panel into a compact icon.
• Reset Button: Single-click to restore all default settings.