Fixes calculations (#2)

Git Level (per commit):
    - Track unique file paths in FilesModified slice
    - FilesChanged = count of unique files in THIS commit

  Aggregator Level (per contributor):
    - Collect all file paths from all commits into a SET
    - FilesChanged = size of the unique file set

  Result:
    - Contributor.FilesChanged = count of UNIQUE files they touched
    - Repository contributor = unique files in THAT repo only

internal/domain/scoring/calculator_test.go

@@ -452,6 +452,8 @@ func TestCalculator_AllAchievementTypes(t *testing.T) {
 						ReviewComments:          25,
 						LinesAdded:              1500,
 						LinesDeleted:            600,
+						MeaningfulLinesAdded:    1500,
+						MeaningfulLinesDeleted:  600,
 						AvgReviewTime:           1.5,
 						UniqueReviewees:         7,
 						RepositoriesContributed: []string{"owner/repo1", "owner/repo2"},