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/alerts/_rule_fields.html

@@ -0,0 +1,29 @@
+{# alerts/_rule_fields.html — HTMX partial: resource + metric selects for a given source_module #}
+<div class="form-group">
+  <label>Resource Name</label>
+  {% if resources %}
+  <select name="resource_name" required>
+    {% if not current_resource %}<option value="" disabled selected>— pick a resource —</option>{% endif %}
+    {% for r in resources %}
+    <option value="{{ r }}" {% if r == current_resource %}selected{% endif %}>{{ r }}</option>
+    {% endfor %}
+  </select>
+  {% else %}
+  <select name="resource_name" required disabled>
+    <option value="">No data yet — run monitors first</option>
+  </select>
+  <p style="font-size:0.78rem;color:var(--text-muted);margin-top:0.25rem;">
+    Resource names populate from live metric data. Start the scheduler and try again.
+  </p>
+  {% endif %}
+</div>
+
+<div class="form-group">
+  <label>Metric Name</label>
+  <select name="metric_name" required>
+    {% if not current_metric %}<option value="" disabled selected>— pick a metric —</option>{% endif %}
+    {% for m in metrics %}
+    <option value="{{ m }}" {% if m == current_metric %}selected{% endif %}>{{ m }}</option>
+    {% endfor %}
+  </select>
+</div>