fix : prevented duplicate entries in _partition_lists case-insensitive comparison

[tmdeveloper007]

Summary of What Has Been Done

Fixed the _partition_lists function in src/utils/roadmap_comparer.py to prevent duplicate entries when the same semantic item appears in both lists with different capitalizations.

The bug caused items like "Python" (list_a) and "python" (list_b) to appear both in the overlapping list AND in the unique_b list, because the unique_b comprehension only checked key not in norm_a without considering that the key had already been claimed as overlapping.

Changes Made

• Modified the unique_b list comprehension in _partition_lists to exclude keys that have already been added to the overlapping list:

  # Before:
  unique_b = [original for key, original in norm_b.items() if key not in norm_a]
  
  # After:
  unique_b = [original for key, original in norm_b.items()
             if key not in norm_a and key not in seen_overlap]

Impact it Made

• Roadmap comparisons no longer contain duplicate skill/topic entries
• Users see clean, non-redundant comparison data
• Fixes data integrity issue in the roadmap comparison feature

Closes #1336

Note: Please assign this PR to the tmdeveloper007 account.

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