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/init.js

@@ -59,11 +59,13 @@
     }
     _dashboardInitialized = true;
     await window.loadServices();
+    await loadTemplateCategories();
     window.buildGrid();
     animateTopCards();
     window.refreshAll();
     setInterval(window.refreshAll, DC.POLL.DASHBOARD);
     if (typeof window.refreshCredsButtons === 'function') window.refreshCredsButtons();
+    if (typeof window.refreshMonitoringWidgets === 'function') window.refreshMonitoringWidgets();
     // Update auth card (may have already been updated by the auto-load IIFE but ensure it's correct)
     if (typeof window._updateAuthCard === 'function') {
       try {
@@ -200,6 +202,55 @@
   window.loadCustomServices = loadCustomServices;
   registerServiceWorker();
 
+  // ===== TEMPLATE CATEGORIES =====
+  // Cached template categories from /api/v1/templates for use across the UI
+  // (service create/edit, filter dropdown, category badges, etc.)
+  async function loadTemplateCategories() {
+    try {
+      const r = await fetch('/api/v1/templates', { cache: 'no-store' });
+      if (!r.ok) return;
+      const data = await r.json();
+      if (data && data.categories) {
+        window.DC_CATEGORIES = data.categories;
+        // Also expose via globals.js constant for convenience
+        if (typeof DC !== 'undefined') DC.CATEGORIES = data.categories;
+        // Populate any category <select> that's already in the DOM
+        populateCategorySelects();
+      }
+    } catch (e) {
+      console.warn('[init] Failed to load template categories:', e);
+    }
+  }
+
+  function populateCategorySelects() {
+    const cats = window.DC_CATEGORIES || (typeof DC !== 'undefined' && DC.CATEGORIES);
+    if (!cats) return;
+    document.querySelectorAll('select[data-role="service-category"]').forEach(select => {
+      const current = select.dataset.current || '';
+      // Clear options but keep the first (placeholder)
+      const placeholder = select.querySelector('option[value=""]');
+      select.innerHTML = '';
+      if (placeholder) select.appendChild(placeholder);
+      else {
+        const ph = document.createElement('option');
+        ph.value = '';
+        ph.textContent = '— Select category —';
+        select.appendChild(ph);
+      }
+      Object.entries(cats).forEach(([name, info]) => {
+        const opt = document.createElement('option');
+        opt.value = name;
+        opt.textContent = `${info.icon || ''} ${name}`.trim();
+        if (name === current) opt.selected = true;
+        select.appendChild(opt);
+      });
+    });
+  }
+
+  // Allow other modules to re-run population after they (re)inject selects
+  window.populateCategorySelects = populateCategorySelects;
+  window.loadTemplateCategories = loadTemplateCategories;
+
   // TOTP-gated initialization
   (async () => {
     try {