Cleans up 22 ruff lint errors discovered by `ruff check --select=E,W,F`:
- F401 unused imports: json, sys, mock, textwrap (8 test files)
- F541 f-strings without placeholders: check_migration_collisions.py
- F841 unused variables: e, posted, old_title, per_context_iterated_for
- E741 ambiguous variable name `l` → `ln` in test_main_red_watchdog.py
All changes are test/script only; no production code affected.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Molecule AI Dev Engineer A (Kimi)
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