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/user.py

@@ -36,3 +36,7 @@ class User(Base):
     notifications = relationship("Notification", back_populates="user", cascade="all, delete-orphan")
     reported_blockers = relationship("Blocker", foreign_keys="Blocker.reported_by", back_populates="reporter")
     resolved_blockers = relationship("Blocker", foreign_keys="Blocker.resolved_by", back_populates="resolver")
+
+    # Automation relationships
+    created_triggers = relationship("Trigger", back_populates="creator")
+    scheduled_reports = relationship("ScheduledReport", back_populates="recipient", cascade="all, delete-orphan")