Redesign The Hub web UI: softer dark theme, sidebar nav, status widgets

Apply the approved "The Hub" redesign to the web admin while keeping every
existing mechanic intact (polling, service-detail modals, Matrix and system
password management, NWC wallet manager, update/rebuild/backup/security/
reboot flows, feature manager, onboarding, role handling).

Layout (templates/index.html):
- Old header bar + IP bar replaced by a sidebar + topbar app shell.
  Sidebar carries the brand (The Hub / Sovran_SystemsOS version), category
  navigation with live counts, the System actions (Update System, Tech
  Support, Manual Backup, Security, node-only Upgrade), Feature Manager /
  Preferences, and the role badge.
- Topbar carries the page title, a service search box, the LAN | WAN
  network chip (external IP always visible, one line), Reboot and Sign Out.
- New widgets row: Systems Operational summary (opens the new Systems
  Operational modal) and Bitcoin Core sync progress with block/ETA.
- New Systems Operational modal: service counts, router port-forwarding
  steps (80/443 to this machine's LAN IP), the live domain diagnostics
  checklist, and which services use those ports.

New static/js/dashboard.js (namespaced IIFE, no new globals) renders the
nav, search filtering, widgets, and the Systems Operational modal; it is
driven by the existing /api/services payloads via a
window.dashboardServicesUpdated() hook called from buildTiles/updateTiles.

Visual design (static/css/*):
- New token set (softer dark surfaces, lifted contrast, Sovran green
  reserved for status and actions) with legacy variable names aliased so
  every secondary sheet re-skins automatically.
- Tiles, dialogs, buttons, inputs, toggles, tables, forms, overlays and
  the login page restyled to the GNOME/libadwaita-flavored surfaces:
  20px cards, 26px dialogs, pill buttons, libadwaita switches, mono value
  pills with Copy buttons, consistent modal anatomy.
- Inline SVG symbol set for chrome/nav icons (monochrome, currentColor);
  service icons still load from /static/icons/*.svg as before.
- Sidebar system buttons now use vector glyphs instead of emoji.

Behavioral details:
- Service detail modal header gains a status pill next to the version
  chip; credentials render with pre-wrap for multiline values.
- First-login security banner now renders as a card inside the content
  area instead of a full-width strip above the app.
- Search + category filtering hide/show sections and tiles without
  touching the polling or update logic.

Onboarding and login pages rebranded to "The Hub" with aligned palette.

app/sovran_systemsos_web/static/js/events.js

@@ -175,9 +175,9 @@ function showSecurityBanner() {
     '</div>' +
     '<button class="security-banner-dismiss" id="security-banner-dismiss-btn" title="Dismiss">\u2715</button>';
 
-  var mainContent = document.querySelector(".main-content");
-  if (mainContent) {
-    mainContent.insertAdjacentElement("beforebegin", banner);
+  var contentArea = document.querySelector(".content");
+  if (contentArea) {
+    contentArea.insertAdjacentElement("afterbegin", banner);
   } else {
     document.body.insertAdjacentElement("afterbegin", banner);
   }