Add fullscreen calibration mode and fix camera preview clipping

[harsshks]

What this PR does

• Adds fullscreen mode during eye-tracking calibration to prevent UI clipping
• Automatically enters fullscreen during training/validation
• Exits fullscreen cleanly on completion or route leave
• Fixes camera preview being clipped by stepper container constraints

Root cause

Camera preview was being clipped by a parent stepper container using
max-height + overflow: hidden.

Fix

• Remove height constraints on stepper container
• Allow natural scrolling
• Add defensive fullscreen API handling

Testing

• Chrome, Edge (desktop)
• Calibration flow: training → validation → completion
• Verified fullscreen enter/exit and no camera cropping

Fixes #100

[harsshks]

✅ Conflicts Resolved & Ready for Review

I've successfully resolved the merge conflicts and updated this PR with the latest changes from main. Here's a summary of what this PR implements:

🎯 Core Features Implemented

1. Fullscreen Calibration Mode

• ✅ Cross-browser support: Chrome, Firefox, Safari, Edge
• ✅ Auto-enter fullscreen when training/validation phases start
• ✅ Auto-exit fullscreen when calibration completes or user navigates away
• ✅ Graceful fallback for browsers that don't support fullscreen API

2. Camera Preview Fixes

• ✅ Resolved cropping issue in CameraConfiguration.vue
• ✅ Removed stepper height constraints that were clipping camera view
• ✅ Improved video element sizing for better compatibility
• ✅ Added natural scrolling when content exceeds viewport