Show which apps are in each backup + optional per-app manual backup

Prompted by today's testing: running backup-k8s-apps.sh --apps X repeatedly
for isolated per-app verification left a bunch of single-app archives in
the list, all named identically (myapps-k8s-backup-TIMESTAMP.tar.gz) with
no visible indication of which app(s) each one actually contains — the
data was already there (the .meta.json sidecar's `apps` field, used for
the status-dot rolling average) but only surfaced in a hover tooltip.
Cleaned up today's test archives (local + VM + R2) and ran one fresh full
backup so the list reflects real state.

Two things added, backup/restore logic itself untouched per explicit
instruction:

1. A small visible badge next to each backup's name — "All apps" for a
   full bundle, or the specific list (e.g. "odoo, n8n") for a partial one
   — in both the Jinja-rendered list and platform.js's refresh path.

2. An optional app-picker on the "Run Backup Now" manual trigger, same
   checkbox-grid pattern already used on the Restore page's app selector.
   All checked (default) = exactly today's existing behavior, no --apps
   flag, everything bundled into one archive. Unchecking some = a
   deliberate one-off partial backup (--apps a,b) for e.g. backing up just
   odoo before a risky change without waiting on the other 4. The nightly
   cron and "backup all together" behavior are completely unaffected —
   this only touches the manual/UI-triggered path.

Verified: manual full backup still produces one bundled archive (249M, 5
apps); the apps-badge renders correctly ("All apps") on the live standby;
the --apps arg-construction logic unit-tested directly (partial selection
-> ['--apps', 'a,b'], all-selected -> [] i.e. default bundle).

platform/static/js/platform.js

@@ -410,11 +410,15 @@ function renderBackupList(items, id, source) {
     const detailsBtn = typeof showBackupDetails === 'function'
       ? `<button class="btn btn-ghost btn-sm" style="color:var(--text3);" onclick="showBackupDetails('${source}','${safe}',this)" title="Quick details"><i class="fas fa-circle-info"></i></button>`
       : '';
+    const appsLabel = (b.apps && b.apps.length)
+      ? `<span class="badge" style="background:rgba(59,130,246,0.12);color:var(--accent2);font-size:10px;white-space:nowrap;">${b.apps.length >= 5 ? 'All apps' : escapeHtml(b.apps.join(', '))}</span>`
+      : '';
     return `
     <div class="backup-item" id="bk-item-${source}-${name.replace(/[^a-z0-9]/gi, '_')}">
       <div class="backup-item-main">
         <span class="status-dot status-dot-${status}" title="${title}"></span>
         <span class="backup-name">${escapeHtml(name)}</span>
+        ${appsLabel}
       </div>
       <div class="backup-actions">
         ${detailsBtn}
@@ -489,7 +493,14 @@ async function runManualBackup() {
   if (wrapper) wrapper.style.display = '';
   if (logEl) logEl.innerHTML = '';
   try {
-    const r = await fetch('/api/backups/run', { method: 'POST' });
+    const selectedApps = Array.from(
+      document.querySelectorAll('#backup-apps-checkbox-group input[type="checkbox"]:checked')
+    ).map((cb) => cb.value);
+    const r = await fetch('/api/backups/run', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ apps: selectedApps }),
+    });
     const d = await r.json();
     if (!d.success) throw new Error(d.message || 'Failed');
     manualBackupJobId = d.job_id;