refactor: extract admin business logic to services, introduce job queue, add derived index helpers

- Move DB operations from routes/admin.py to services/admin.py (get_logs_context, query_summary_statuses, retry_failed, delete/reset operations)
- Add services/jobs.py with Job/JobEvent-based async job queue (create_job, run_job, enqueue_job)
- Add services/derived.py with FTS5 reindex and paper index deletion helpers
- Refactor scheduler to use job queue instead of direct pipeline calls
- Add heartbeat_at/expires_at to TaskLock for lock health tracking
- Remove DESIGN_REVIEW.md
- Update tests: remove redundant integration tests, add unit tests for new services

app/models.py

@@ -32,6 +32,26 @@ class SummaryState(StrEnum):
     PERMANENT_FAILURE = "permanent_failure"
 
 
+class JobStatus(StrEnum):
+    """后台任务状态枚举 — 对应 jobs.status 列。"""
+
+    QUEUED = "queued"
+    RUNNING = "running"
+    SUCCESS = "success"
+    FAILED = "failed"
+    STALE = "stale"
+    CANCELLED = "cancelled"
+
+
+class JobEventStatus(StrEnum):
+    """任务阶段事件状态枚举 — 对应 job_events.status 列。"""
+
+    STARTED = "started"
+    SUCCESS = "success"
+    FAILED = "failed"
+    INFO = "info"
+
+
 # ── papers ──────────────────────────────────────────────────────────────
 class Paper(Base):
     __tablename__ = "papers"
@@ -194,9 +214,48 @@ class TaskLock(Base):
     status = Column(String, nullable=False)
     owner = Column(String)
     acquired_at = Column(DateTime, nullable=False)
+    heartbeat_at = Column(DateTime)
+    expires_at = Column(DateTime)
     released_at = Column(DateTime)
 
 
+# ── jobs / job_events ──────────────────────────────────────────────────
+class Job(Base):
+    __tablename__ = "jobs"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    type = Column(String, nullable=False, index=True)
+    status = Column(String, nullable=False, default=JobStatus.QUEUED, index=True)
+    owner = Column(String)
+    payload_json = Column(Text)
+    result_json = Column(Text)
+    error = Column(Text)
+    created_at = Column(DateTime, nullable=False)
+    started_at = Column(DateTime)
+    heartbeat_at = Column(DateTime)
+    completed_at = Column(DateTime)
+
+    events = relationship(
+        "JobEvent", back_populates="job", cascade="all, delete-orphan"
+    )
+
+
+class JobEvent(Base):
+    __tablename__ = "job_events"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    job_id = Column(
+        Integer, ForeignKey("jobs.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    stage = Column(String, nullable=False)
+    status = Column(String, nullable=False)
+    message = Column(Text)
+    payload_json = Column(Text)
+    created_at = Column(DateTime, nullable=False)
+
+    job = relationship("Job", back_populates="events")
+
+
 # ── user data ──────────────────────────────────────────────────────────
 class UserBookmark(Base):
     __tablename__ = "user_bookmarks"