fix: preview enum 누락 + AI summary thinking 제거 + CLAUDE.md 전면 갱신

- queue.py: process_stage enum에 'preview' 추가
- classify_worker: ai_summary에 strip_thinking() 적용
- CLAUDE.md: 현재 아키텍처 전면 반영 (파이프라인, UI, 인프라, 코딩규칙)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/models/queue.py

@@ -14,7 +14,7 @@ class ProcessingQueue(Base):
     id: Mapped[int] = mapped_column(BigInteger, primary_key=True)
     document_id: Mapped[int] = mapped_column(BigInteger, ForeignKey("documents.id"), nullable=False)
     stage: Mapped[str] = mapped_column(
-        Enum("extract", "classify", "embed", name="process_stage"), nullable=False
+        Enum("extract", "classify", "embed", "preview", name="process_stage"), nullable=False
     )
     status: Mapped[str] = mapped_column(
         Enum("pending", "processing", "completed", "failed", name="process_status"),