Make Manual Backup match the system role (Desktop Only scope)

The Manual Backup screen in the Hub always listed the Node / Server +
Desktop items (nix-bitcoin secrets, /var/lib system service data, and the
database/blockchain caveat), and the backup script mirrored /var/lib and
counted it in the free-space estimate even on the Desktop Only role.
Desktop Only systems run no server or Bitcoin services and have no
internal second data drive, so none of that applies.

Hub UI (support.js):
- 'What gets backed up' is role-aware: Desktop Only lists only the NixOS
  configuration (/etc/nixos) and home directory (/home)
- Database/blockchain note hidden on Desktop Only
- Intro copy corrected: external USB copy is a second location on
  Desktop Only (no internal second drive); third-location wording kept
  for Node / Server + Desktop

Backup script (sovran-hub-backup.sh):
- Desktop Only runs 2 stages (1/2 /etc/nixos, 2/2 /home); secrets and
  /var/lib stages no longer run on that role
- Free-space estimate skips /var/lib on Desktop Only
- BACKUP_MANIFEST.txt sources/exclusions/limitations/restore guidance
  and blockchain note are role-aware
- Completion message role-aware ('second, external location' on
  Desktop Only); header comments updated

Node and Server + Desktop behavior is unchanged. Added CHANGELOG entry.

Verified: bash -n / node --check, 6 role-detection cases, manifest
generation for both role groups (non-desktop output identical to
before), and simulated UI renders for all three roles.

Co-authored-by: arena-agent <297053741+arena-agent@users.noreply.github.com>

app/sovran_systemsos_web/static/js/support.js

@@ -473,19 +473,73 @@ function renderBackupReady(drives) {
     ].join("");
   }
 
+  // ── Role-aware backup description ─────────────────────────────
+  // Desktop Only systems run no server or Bitcoin services and have no
+  // internal second drive, so the backup mirrors only the NixOS configuration
+  // and home directory. nix-bitcoin secrets, /var/lib system service data,
+  // and the database/blockchain caveats apply only to the Node and
+  // Server + Desktop roles.
+  var isDesktopOnly = (_currentRole === "desktop");
+
+  var introHtml;
+  if (isDesktopOnly) {
+    introHtml = [
+      '<div class="support-wallet-box support-wallet-protected" style="margin-bottom:16px;">',
+        '<p class="support-wallet-desc">',
+          'This manual backup lets you create a copy of your system on an external USB drive \u2014 ',
+          'storing your data in a second location, outside the computer, for maximum protection ',
+          'against hardware failure or physical damage.',
+        '</p>',
+      '</div>',
+    ].join("");
+  } else {
+    introHtml = [
+      '<div class="support-wallet-box support-wallet-protected" style="margin-bottom:16px;">',
+        '<p class="support-wallet-desc">',
+          'Your Sovran Pro already backs up your data automatically to its internal second drive. ',
+          'This manual backup lets you create an additional copy on an external USB drive \u2014 ',
+          'storing your data in a third location, outside the computer, for maximum protection ',
+          'against hardware failure or physical damage.',
+        '</p>',
+      '</div>',
+    ].join("");
+  }
+
+  var backupItemsHtml;
+  if (isDesktopOnly) {
+    backupItemsHtml = [
+      '<li>NixOS configuration (<code>/etc/nixos</code>)</li>',
+      '<li>Home directory (<code>/home</code>)</li>',
+    ].join("");
+  } else {
+    backupItemsHtml = [
+      '<li>NixOS configuration (<code>/etc/nixos</code>)</li>',
+      '<li>nix-bitcoin secrets (<code>/etc/nix-bitcoin-secrets</code>)</li>',
+      '<li>System service data (<code>/var/lib</code>) — excluding databases and blockchain data (see note below)</li>',
+      '<li>Home directory (<code>/home</code>)</li>',
+    ].join("");
+  }
+
+  // The database/blockchain caveat is only relevant when server services exist.
+  var dbNoteHtml = "";
+  if (!isDesktopOnly) {
+    dbNoteHtml = [
+      '<div class="support-wallet-box support-wallet-warning">',
+        '<div class="support-wallet-header">',
+          '<span class="support-wallet-icon">\u2139\ufe0f</span>',
+          '<span class="support-wallet-title">Database and Blockchain Data</span>',
+        '</div>',
+        '<p class="support-wallet-desc">Application databases stored in PostgreSQL or MariaDB/MySQL are <strong>not included</strong> in Manual Backup. Bitcoin blockchain and Electrs index data are also excluded (they are stored on the internal second drive). If you use Nextcloud, Matrix, or other database-backed applications, back up those databases separately with their native tools.</p>',
+      '</div>',
+    ].join("");
+  }
+
   $supportBody.innerHTML = [
     '<div class="support-section">',
     '<div class="support-icon-big">\ud83d\udcbe</div>',
     '<h3 class="support-heading">Manual Backup</h3>',
 
-    '<div class="support-wallet-box support-wallet-protected" style="margin-bottom:16px;">',
-      '<p class="support-wallet-desc">',
-        'Your Sovran Pro already backs up your data automatically to its internal second drive. ',
-        'This manual backup lets you create an additional copy on an external USB drive \u2014 ',
-        'storing your data in a third location, outside the computer, for maximum protection ',
-        'against hardware failure or physical damage.',
-      '</p>',
-    '</div>',
+    introHtml,
 
     '<div class="support-steps">',
       '<div class="support-steps-title">Requirements</div>',
@@ -500,20 +554,11 @@ function renderBackupReady(drives) {
     '<div class="support-steps">',
       '<div class="support-steps-title">What gets backed up</div>',
       '<ol class="support-backup-steps">',
-        '<li>NixOS configuration (<code>/etc/nixos</code>)</li>',
-        '<li>nix-bitcoin secrets (<code>/etc/nix-bitcoin-secrets</code>)</li>',
-        '<li>System service data (<code>/var/lib</code>) — excluding databases and blockchain data (see note below)</li>',
-        '<li>Home directory (<code>/home</code>)</li>',
+        backupItemsHtml,
       '</ol>',
     '</div>',
 
-    '<div class="support-wallet-box support-wallet-warning">',
-      '<div class="support-wallet-header">',
-        '<span class="support-wallet-icon">\u2139\ufe0f</span>',
-        '<span class="support-wallet-title">Database and Blockchain Data</span>',
-      '</div>',
-      '<p class="support-wallet-desc">Application databases stored in PostgreSQL or MariaDB/MySQL are <strong>not included</strong> in Manual Backup. Bitcoin blockchain and Electrs index data are also excluded (they are stored on the internal second drive). If you use Nextcloud, Matrix, or other database-backed applications, back up those databases separately with their native tools.</p>',
-    '</div>',
+    dbNoteHtml,
 
     '<div class="support-wallet-box support-wallet-protected">',
       '<div class="support-wallet-header">',