Function calculate_tech_debt 

pub fn calculate_tech_debt(
    events: &[&GitEvent],
    get_files: impl Fn(&str) -> Option<Vec<String>>,
    min_commits: usize,
) -> TechDebtAnalysis

Calculate technical debt score

Technical debt = change frequency x complexity x age

Formula:

• Churn score: (change_count / max_change_count)
• Complexity score: (lines_changed / max_lines_changed)
• Age score: (days_elapsed / 365) capped at 1.0