Replace TODO comments in DuplicatesModule with real implementation or remove

[iliyami]

Audit the codebase for // TODO, // FIXME, and // XXX comments. For each one:

• If trivial: implement the fix
• If complex: convert to a tracked GitHub issue and link it from the code
• If stale: delete the comment

How to find them

grep -rn 'TODO\|FIXME\|XXX' Sources/ --include='*.swift'

Acceptance

No unannotated TODOs remain in the codebase.