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/core/alerts.py

@@ -5,7 +5,7 @@ import uuid
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING
 
-from sqlalchemy import select
+from sqlalchemy import and_, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from fabledscryer.models.alerts import (
@@ -14,6 +14,7 @@ from fabledscryer.models.alerts import (
     AlertRule,
     AlertState,
     AlertStateEnum,
+    MaintenanceWindow,
 )
 from fabledscryer.models.metrics import PluginMetric
 
@@ -60,6 +61,26 @@ async def record_metric(
     session.add(metric)
     await session.flush()
 
+    # Check active maintenance windows — skip rule evaluation if suppressed
+    mw_result = await session.execute(
+        select(MaintenanceWindow).where(
+            MaintenanceWindow.start_at <= now,
+            MaintenanceWindow.end_at >= now,
+            or_(
+                MaintenanceWindow.scope_source.is_(None),
+                and_(
+                    MaintenanceWindow.scope_source == source_module,
+                    or_(
+                        MaintenanceWindow.scope_resource.is_(None),
+                        MaintenanceWindow.scope_resource == resource_name,
+                    ),
+                ),
+            ),
+        ).limit(1)
+    )
+    if mw_result.scalar_one_or_none() is not None:
+        return  # suppressed by maintenance window
+
     # Load matching enabled rules
     result = await session.execute(
         select(AlertRule).where(