fix: pass actual t1w files to summary interface

[mgxd]

Summary should receive the actual T1w files found, not a phony source file

Closes #3530

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.98%. Comparing base (d28596f) to head (5a1100f).
⚠️ Report is 2 commits behind head on maint/25.2.x.

Additional details and impacted files

@@               Coverage Diff                @@
##           maint/25.2.x    #3545      +/-   ##
================================================
- Coverage         73.05%   72.98%   -0.07%     
================================================
  Files                60       60              
  Lines              4813     4813              
  Branches            624      624              
================================================
- Hits               3516     3513       -3     
- Misses             1156     1158       +2     
- Partials            141      142       +1     

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