feat: implement automation module

- Event-based triggers (Phase 1):
  - Trigger/TriggerLog models with field_change type
  - TriggerService for condition evaluation and action execution
  - Trigger CRUD API endpoints
  - Task integration (status, assignee, priority changes)
  - Frontend: TriggerList, TriggerForm components

- Weekly reports (Phase 2):
  - ScheduledReport/ReportHistory models
  - ReportService for stats generation
  - APScheduler for Friday 16:00 job
  - Report preview/generate/history API
  - Frontend: WeeklyReportPreview, ReportHistory components

- Tests: 23 new tests (14 triggers + 9 reports)
- OpenSpec: add-automation change archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/models/report_history.py

@@ -0,0 +1,28 @@
+import uuid
+import enum
+from sqlalchemy import Column, String, Text, DateTime, ForeignKey, Enum, JSON
+from sqlalchemy.sql import func
+from sqlalchemy.orm import relationship
+from app.core.database import Base
+
+
+class ReportHistoryStatus(str, enum.Enum):
+    SENT = "sent"
+    FAILED = "failed"
+
+
+class ReportHistory(Base):
+    __tablename__ = "pjctrl_report_history"
+
+    id = Column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    report_id = Column(String(36), ForeignKey("pjctrl_scheduled_reports.id", ondelete="CASCADE"), nullable=False)
+    generated_at = Column(DateTime, server_default=func.now(), nullable=False)
+    content = Column(JSON, nullable=False)
+    status = Column(
+        Enum("sent", "failed", name="report_history_status_enum"),
+        nullable=False
+    )
+    error_message = Column(Text, nullable=True)
+
+    # Relationships
+    report = relationship("ScheduledReport", back_populates="history")