fix(webui/backups): sync fleet Backups sub-tab URLs (/apps/overview/backups/<sub>)

The embedded backup center deep-links *in* fine (mountBackupCenter parses the
sub-segment), but clicking a sub-tab never wrote the URL: BackupPage disables
pushTabToUrl() when embedded and nothing on the fleet side stepped in, so the
address bar stayed stale and the sub-tabs weren't shareable/deep-linkable —
unlike the sibling Migrate sub-tabs.

Give BackupPage an onTabChange hook fired on every switch; the OverviewManager
supplies it to replaceState /apps/overview/backups/<sub> (replaceState, matching
Migrate, so the on-entry deep-link re-sync can't stack a duplicate history
entry). Standalone /backup keeps using pushTabToUrl() unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Signed-off-by: librelad <librelad@digitalangels.vip>

containers/libreportal/frontend/components/apps/overview/js/overview-manager.js

@@ -643,7 +643,16 @@ class OverviewManager {
         return;
       }
       try { if (window.overviewBackupPage) window.overviewBackupPage.dispose(); } catch (_) {}
-      window.overviewBackupPage = new BackupPage({ embedded: true });
+      // Own the URL for the embedded center's sub-tabs: reflect each switch as
+      // /apps/overview/backups/<sub> so they're shareable + deep-linkable (the
+      // read side is already handled by mountBackupCenter's segment parse). Use
+      // replaceState, mirroring the Migrate sub-tabs — the switchTab() we fire
+      // on entry to honor a deep link would otherwise stack a duplicate history
+      // entry on top of the one we navigated in on.
+      window.overviewBackupPage = new BackupPage({
+        embedded: true,
+        onTabChange: (sub) => this._pushUrl(`/apps/overview/backups/${sub}`, true),
+      });
       await window.overviewBackupPage.init();
       if (sub) { try { window.overviewBackupPage.switchTab(sub); } catch (_) {} }
     } catch (_) {

containers/libreportal/frontend/components/backup/core/js/backup-page.js

@@ -8,8 +8,14 @@
 class BackupPage {
     constructor(opts = {}) {
         // Embedded in the fleet Overview's Backups tab: the same controller, but
-        // it must not couple to the /backup URL (the fleet owns /overview/backups).
+        // it must not write the standalone /backup URL — the fleet owns the
+        // address bar. It hands us onTabChange so a sub-tab switch still syncs the
+        // canonical /apps/overview/backups/<sub> URL via the OverviewManager.
         this.embedded = !!opts.embedded;
+        // Host-supplied when embedded: called with the new sub-tab slug after
+        // every switch so the host can reflect it in the URL. Null for the
+        // standalone page, which uses pushTabToUrl() instead.
+        this.onTabChange = typeof opts.onTabChange === 'function' ? opts.onTabChange : null;
         this.currentTab = 'dashboard';
         this.dashboard = null;
         this.locations = null;
@@ -37,7 +43,10 @@ class BackupPage {
        and /backup?backup=dashboard (standard query string) so links from
        either source resolve correctly. */
     parseTabFromUrl() {
-        if (this.embedded) return null;   // embedded: always open on Dashboard; sub-tabs are in-page only
+        // Embedded: the fleet host (OverviewManager.mountBackupCenter) parses the
+        // /apps/overview/backups/<sub> segment and drives switchTab, so the
+        // embedded controller never reads the URL itself.
+        if (this.embedded) return null;
         const allowed = new Set(['dashboard', 'backups', 'locations', 'configuration']);
         // Path-based: /backup/<tab> (bare /backup → default tab).
         const seg = window.location.pathname.replace(/^\/backup\/?/, '').split('/')[0];
@@ -339,11 +348,18 @@ class BackupPage {
         this.currentTab = tab;
         this.applyActiveTabUi(tab);
         this.updatePrimaryAction();
-        if (!opts.fromPopstate) this.pushTabToUrl(tab);
+        if (!opts.fromPopstate) {
+            // Standalone writes /backup/<tab> itself; embedded lets the fleet host
+            // map the switch onto /apps/overview/backups/<tab> via onTabChange (its
+            // own pushTabToUrl is a no-op). Both are skipped when the switch was
+            // triggered by a popstate — the URL has already moved.
+            this.pushTabToUrl(tab);
+            if (this.onTabChange) { try { this.onTabChange(tab); } catch (_) {} }
+        }
     }
 
     pushTabToUrl(tab) {
-        if (this.embedded) return;        // embedded: keep the URL at /overview/backups (no sub-tab coupling)
+        if (this.embedded) return;        // embedded: the fleet host owns the URL (see onTabChange)
         const url = `/backup/${tab}`;
         // Use replaceState for the *first* push (initial tab inferred from
         // URL); otherwise pushState so back/forward navigates between tabs.