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/dashboard.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 from datetime import datetime, timezone
-from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, String
+from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, String, Text
 from sqlalchemy.orm import Mapped, mapped_column
 from .base import Base
 
@@ -51,3 +51,5 @@ class DashboardWidget(Base):
     )
     widget_key: Mapped[str] = mapped_column(String(64), nullable=False)
     position: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    title: Mapped[str | None] = mapped_column(String(128), nullable=True)
+    config_json: Mapped[str | None] = mapped_column(Text, nullable=True)