Add category completion ratios to NeetCode Mastery Dashboard

[Rowrow620]

First Timers Only

This issue is reserved for developers who are new to AlgoBuddy or open-source contributing. We know that submitting a first pull request can feel intimidating. The goal of this issue is to guide you step-by-step through making your first contribution to the AlgoBuddy repository.

Description of the Issue

On the NeetCode 150 Mastery Dashboard, category headers display the topic title (e.g. "Arrays & Hashing"), but do not show how many problems within that category have been completed.

Proposed Solution

Display completion ratios (e.g. Arrays & Hashing (9/9), Two Pointers (5/5)) inside each category header card on the dashboard.

Implementation Steps

1. Open src/app.rs and locate render_dashboard.
2. For each category card, calculate the completed problem count:

   let completed_count = category_problems
       .iter()
       .filter(|p| self.completed_problems.contains(&p.id()))
       .count();
   let total_count = category_problems.len();
   
   let title_text = format!("{} ({}/{})", category.name(), completed_count, total_count);
   ui.heading(RichText::new(title_text).color(p.cyan).strong());
   

Acceptance Criteria

To merge a pull request for this issue:

• Code Formatting: cargo fmt --all -- --check completes without warnings.
• All Tests Pass: cargo test passes 100% of unit tests.
• Issue Solved: The implementation fully addresses the requirements described above.
• Clean Git Branch: Changes are committed to a feature branch targeting dev.

Step-by-Step Contribution Guide

1. Claim this issue: Comment below that you are working on this issue to receive assignment.
2. Fork and Branch: Create a new branch off dev named issue-[id]-[feature-name].
3. Make and Test Changes: Run cargo fmt --all and cargo test locally to verify build health.
4. Submit PR: Push your branch to GitHub and create a Pull Request targeting the dev branch.

Additional Information

• Contributing Guide
• README