Add confirmation dialog before resetting dashboard progress

[dyson-025]

Description

This PR adds a confirmation dialog before resetting the NeetCode Dashboard progress.

Instead of immediately clearing all completed problem checkmarks, clicking Reset All Progress now opens a confirmation dialog. Users can either cancel the action or confirm the reset, helping prevent accidental loss of progress.

Related Issues

Closes #13

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New problem visualizer audit / promotion (AuditStatus::Audited)
• New feature (non-breaking change adding functionality)
• Documentation update
• Refactoring / performance optimization

Verification Checklist

• Code compiles cleanly without errors
• cargo test passes 100% of unit tests
• cargo fmt --all -- --check complies with standard Rust formatting
• cargo clippy --all-targets -- -D warnings produces zero warnings
• Step visualizer tested locally in desktop mode (cargo run) and/or WebAssembly mode (trunk serve)

[Rowrow620]

Thanks for working on this!
Tested this out locally and made a few small adjustments. Let me know what you think about these changes!

• Added .anchor(CENTER_CENTER, ...) so egui doesn't stick it in the top-left corner.
• Styled the reset button red/bold so users don't mix it up with Cancel.
• Fixed a double-render issue where render_reset_confirm_modal was being called twice per frame when the dashboard was active.
• Swapped the outer if for an early return guard clause.

Code for src/app.rs:

fn render_reset_confirm_modal(&mut self, ctx: &egui::Context) {
    if !self.show_reset_confirm_modal {
        return;
    }

egui::Window::new("Confirm Reset")
      .collapsible(false)
      .resizable(false)
      .anchor(egui::Align2::CENTER_CENTER, [0.0, 0.0])
      .show(ctx, |ui| {
          ui.label("Are you sure you want to reset all completed problem checkmarks?");
          ui.add_space(8.0);
  
          ui.horizontal(|ui| {
              if ui.button("Cancel").clicked() {
                  self.show_reset_confirm_modal = false;
              }
  
              let dark_red = Color32::from_rgb(210, 40, 65);
              let confirm_btn = egui::Button::new(
                  RichText::new("Confirm Reset").color(Color32::WHITE).strong()
              )
              .fill(dark_red);
  
              if ui.add(confirm_btn).clicked() {
                  self.completed_problems.clear();
                  self.show_reset_confirm_modal = false;
              }
          });
      });

[Rowrow620]

Looks great! The centered window positioning and destructive red button styling look great, and the guard clause keeps the code super clean.

Approved and ready to merge!