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/templates/settings/_tabs.html

@@ -4,6 +4,8 @@
   {% set tabs = [
     ("general",       "General",        "/settings/general/"),
     ("notifications", "Notifications",  "/settings/notifications/"),
+    ("reports",       "Reports",        "/settings/reports/"),
+    ("auth",          "Auth",           "/settings/auth/"),
     ("ansible",       "Ansible",        "/settings/ansible/"),
     ("plugins",       "Plugins",        "/settings/plugins/"),
   ] %}