Optimize git status bucket classification

[joshua-cyberclout]

Summary

This PR reduces per-file work in the Git status aggregation hot path by replacing repeated enum bucket scans with direct bitmask checks.

Why this helps

GitRepositoryStatus.Add was iterating through every FileStatus bucket for every file and calling HasFlag on each bucket. For larger repos, that multiplies the cost of status refreshes with little benefit because the underlying flags are already bit values.

This change preserves the same status buckets while removing repeated enum evaluation in the hot path.

Performance opportunities identified

1. Replace repeated HasFlag checks in GitRepositoryStatus.Add with bitwise status checks.
2. Avoid repeated status dictionary lookups when enumerating file statuses.
3. Reduce per-file allocations in the repository status pipeline.
4. Reuse cached status results across file tree refreshes when nothing changed.
5. Batch git status parsing instead of processing entries one-by-one in tight loops.
6. Defer expensive rename/detail resolution until the UI actually requests it.
7. Avoid converting raw Git status values to string representations earlier than needed.
8. Localize file-status aggregation to the Git integration layer instead of repeating the same work in UI models.
9. Cache folder-level summaries for large directory trees with many unchanged files.
10. Streamline file explorer refresh triggers to avoid redundant status recalculation.

Validation

• Added a regression test covering a combined-status entry (RenamedInIndex | ModifiedInWorkdir) to ensure the bucketed status behavior remains unchanged.
• Full .NET validation is still blocked in this environment by the repo's private NuGet source and Windows SDK requirements, so a Windows-capable build environment is still needed for CI confirmation.

Risk

Low: this is a hot-path optimization only; no user-facing status semantics are changed.

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