fix(study): Phase 1 migrations 222-225 → 226-229 — markdown canonical layer 222 충돌 회피

타 PR (markdown canonical layer Phase 1B) 의 222_processing_queue_stage_markdown.sql 와
번호 충돌. init_db 가 'migration 버전 중복' 에러 띄움. 4파일 + SQL 헤더 주석 일괄 rename.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations/228_progress_topic_pattern_idx.sql

@@ -0,0 +1,5 @@
+-- 228_progress_topic_pattern_idx.sql
+-- 패턴별 필터 — chronic/regressed/recovered 탭 조회 빠르게.
+
+CREATE INDEX IF NOT EXISTS idx_progress_topic_pattern
+    ON study_question_progress (user_id, study_topic_id, pattern_state);