feat: service categories end-to-end + monitoring widgets on main dashboard

Service categories (described in README roadmap, never wired):
- Backend: POST /services now persists category/containerId/port/ip/tailscaleOnly
- Backend: POST /services/update accepts category for in-place changes
- Frontend: category <select> in add-service modal (local + external)
- Frontend: category <select> in edit-service modal with current value
- Frontend: All Categories dropdown in service filter bar (auto-populated
  from both API categories and any categories present on rendered cards)
- Frontend: colored category badge (icon + name) on service cards
- Frontend: filter auto-refreshes after buildGrid

Monitoring on main dashboard (replaces orphaned monitoring-dashboard.html):
- New monitoring-widgets.js embeds a 5-card System Overview panel above
  the filter bar: Services, Containers Up, Avg CPU, Avg Memory, Health
- Pulls /api/v1/monitoring/stats + /api/v1/health-checks/status
- Auto-refreshes on DC.POLL.STATS (5s), color-coded bars (warn >=65%, bad >=85%)

Build:
- Added monitoring-widgets.js to init.js bundle in build.js
- Rebuilt dist/ bundles (core.js, features.js, init.js)
- sw.js cache version bumped automatically
- CSP hash regenerated

status/js/core/service-crud.js

@@ -19,6 +19,16 @@
     document.getElementById('edit-tailscale-only').checked = service.tailscaleOnly || false;
     document.getElementById('edit-logo-url').value = service.logo || '';
 
+    // Populate the category select for this service, then set the current value.
+    // populateCategorySelects() uses data-current so we set it first, then call.
+    const categorySelect = document.getElementById('edit-service-category');
+    if (categorySelect) {
+      categorySelect.dataset.current = service.category || '';
+      if (typeof window.populateCategorySelects === 'function') {
+        window.populateCategorySelects();
+      }
+    }
+
     modal.classList.add('show');
   }
 
@@ -36,6 +46,7 @@
     const newIp = document.getElementById('edit-ip').value.trim() || 'localhost';
     const tailscaleOnly = document.getElementById('edit-tailscale-only').checked;
     const newLogo = document.getElementById('edit-logo-url').value.trim();
+    const newCategory = document.getElementById('edit-service-category')?.value || '';
 
     if (!newSubdomain) {
       showNotification('Subdomain is required', 'warning');
@@ -51,6 +62,7 @@
     if (newIp !== currentEditService.ip) changes.push('ip');
     if (tailscaleOnly !== (currentEditService.tailscaleOnly || false)) changes.push('tailscale');
     if (newLogo && newLogo !== currentEditService.logo) changes.push('logo');
+    if (newCategory !== (currentEditService.category || '')) changes.push('category');
 
     if (changes.length === 0) {
       closeServiceEditModal();
@@ -72,7 +84,8 @@
           port: newPort || currentEditService.port,
           ip: newIp,
           tailscaleOnly,
-          logo: newLogo || undefined
+          logo: newLogo || undefined,
+          category: newCategory
         })
       });
 
@@ -91,7 +104,8 @@
           port: newPort || window.APPS[appIndex].port,
           ip: newIp,
           tailscaleOnly,
-          logo: newLogo || window.APPS[appIndex].logo
+          logo: newLogo || window.APPS[appIndex].logo,
+          category: newCategory || undefined
         };
       }