Add Visual Progress Bars

[Technical-1]

Priority: Medium
Labels: ui, enhancement

Description:
Add progress bars for CPU usage percentage, memory usage (used/total), and disk usage per disk. Use egui::ProgressBar widget.

Files to modify:

• src/main.rs

Acceptance criteria:

• CPU usage progress bar added
• Memory usage progress bar added
• Disk usage progress bars added (one per disk)
• Progress bars update with refresh interval
• Progress bars are visually appealing

Implementation notes:

• Use egui::ProgressBar::new(0.0..=100.0) for CPU
• Use egui::ProgressBar::new(0.0..=total) for memory/disk
• Set progress value based on current usage
• Consider color-coding based on thresholds
• Add labels showing percentage values