feat: implement lazy-load for git stats

[androidZzT]

Background

PR #8 removed the synchronous collectGitStats() subprocess call that was forking git log --numstat for every session during refresh — the single biggest performance bottleneck.

Git stats fields (gitCommits, gitAdditions, gitDeletions) are currently hardcoded to 0. The data model is preserved.

Requirements

• Implement lazy-loading of git stats (load on demand, not during initial refresh)
• Consider async/background loading to avoid blocking the main thread
• Cache results to avoid redundant subprocess calls
• Update UI to show git stats when available

References

• PR perf: remove synchronous collectGitStats() subprocess #8: perf: remove synchronous collectGitStats() subprocess #8