feat(publish): P0-2 발행 read API /published/feed (study→viewer pull-sync)

뷰어가 published 테이블을 rev 커서로 incremental pull 하는 read-only feed.
- GET /published/feed?since={rev}&kind=&limit= → rev>since ORDER BY rev ASC LIMIT(cap 500)
- Bearer(viewer_sync_token) default-deny + 상수시간 비교(internal_study 패턴 재사용)
- 엔벨로프 schema_version + items[pub_id·kind·source_id·rev·deleted·schema_version·payload]
  + next_since·has_more. tombstone(deleted=true) 1급 이벤트 포함.
- viewer_sync_token = Mac mini internal_worker_token 과 분리(폭발반경 격리), 기본 ""=default-deny.

rev 커서 안전 = 워커 단일 라이터(advisory lock) 배치 원자 커밋. 배포는 P0 seam
(P0-3 뷰어 pull-sync) 완성 후 일괄 게이트. read API = additive.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/core/config.py

@@ -191,6 +191,9 @@ class Settings(BaseModel):
     # internal endpoint Bearer token (Mac mini derived-worker 호출용)
     internal_worker_token: str = ""
 
+    # 뷰어↔DS 발행 채널 Bearer token (publish read API P0-2 + ingest P2). Mac mini 토큰과 분리(폭발반경 격리).
+    viewer_sync_token: str = ""
+
 
 def load_settings() -> Settings:
     """config.yaml + 환경변수에서 설정 로딩"""
@@ -200,6 +203,7 @@ def load_settings() -> Settings:
     study_card_extract_enabled = os.getenv("STUDY_CARD_EXTRACT_ENABLED", "true").lower() in ("1", "true", "yes")
     study_publish_enabled = os.getenv("STUDY_PUBLISH_ENABLED", "false").lower() in ("1", "true", "yes")
     internal_worker_token = os.getenv("INTERNAL_WORKER_TOKEN", "")
+    viewer_sync_token = os.getenv("VIEWER_SYNC_TOKEN", "")
     jwt_secret = os.getenv("JWT_SECRET", "")
     totp_secret = os.getenv("TOTP_SECRET", "")
     eval_runner_token = os.getenv("EVAL_RUNNER_TOKEN", "")
@@ -334,6 +338,7 @@ def load_settings() -> Settings:
         study_card_extract_enabled=study_card_extract_enabled,
         study_publish_enabled=study_publish_enabled,
         internal_worker_token=internal_worker_token,
+        viewer_sync_token=viewer_sync_token,
         pipeline_held_stages=pipeline_held_stages,
         mlx_gate_concurrency=mlx_gate_concurrency,
         digest_llm_timeout_s=digest_llm_timeout_s,