feat: maintenance windows, reports, uptime widget, alert improvements

- Add maintenance window scheduling to suppress alerts during planned
  downtime (model, routes, templates)
- Add weekly email/webhook reports with host summary (core/reports.py,
  Settings → Reports tab)
- Add host uptime history widget with per-check sparkline view
- Expand alert rules: dynamic metric catalog for plugin sources,
  per-rule HTMX field loading, maintenance window awareness
- Register additional dashboard widgets (uptime, SNMP, UniFi, UPS)
- Add Settings → Reports tab configuration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fabledscryer/models/alerts.py

@@ -62,6 +62,24 @@ class AlertState(Base):
     acknowledged_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
 
 
+class MaintenanceWindow(Base):
+    __tablename__ = "maintenance_windows"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    name: Mapped[str] = mapped_column(String(128), nullable=False)
+    start_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    end_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    # Scope — null means "all". scope_resource requires scope_source to be set.
+    scope_source: Mapped[str | None] = mapped_column(String(64), nullable=True)
+    scope_resource: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    created_by: Mapped[str] = mapped_column(
+        String(36), ForeignKey("users.id", ondelete="RESTRICT"), nullable=False
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc)
+    )
+
+
 class AlertEvent(Base):
     __tablename__ = "alert_events"