ui(backup): replace delete-location native confirm() with the backup-modal pattern

The inline "Delete location" action was the last spot on the Backup
page still using the native browser confirm() — the snapshot delete
already uses the styled backup-modal, so the location delete sat out
as the odd one. Adds a new #backup-delete-location-modal matching the
existing modal shell (header / body / backup-danger-btn footer),
swaps deleteInlineLocation() to open it instead of confirm(), and
wires the confirm button to a new confirmDeleteLocation() that does
the actual `libreportal backup location remove <idx>` task.

Behaviour is the same — confirm body text moves into the modal as a
muted hint paragraph using backup-card-hint, location name bolded
for scannability. expandedLocs cleanup also moves into the confirm
handler so the row collapses only when the user actually deletes.

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

containers/libreportal/frontend/html/backup-content.html

@@ -216,6 +216,20 @@
   </div>
 </div>
 
+<div class="backup-modal" id="backup-delete-location-modal">
+  <div class="backup-modal-inner">
+    <div class="backup-modal-header">
+      <h3>Delete backup location</h3>
+      <button class="backup-modal-close" data-close-modal>×</button>
+    </div>
+    <div class="backup-modal-body" id="backup-delete-location-modal-body"></div>
+    <div class="backup-modal-footer">
+      <button class="backup-secondary-btn" data-close-modal>Cancel</button>
+      <button class="backup-danger-btn" id="backup-delete-location-confirm">Delete location</button>
+    </div>
+  </div>
+</div>
+
 <div class="backup-modal" id="backup-migrate-modal">
   <div class="backup-modal-inner">
     <div class="backup-modal-header">

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

@@ -293,6 +293,7 @@ class BackupPage {
             if (e.target.closest('#backup-migrate-confirm')) { this.confirmMigrate(); return; }
             if (e.target.closest('#backup-restore-confirm')) { this.confirmRestore(); return; }
             if (e.target.closest('#backup-delete-confirm'))  { this.confirmDelete();  return; }
+            if (e.target.closest('#backup-delete-location-confirm')) { this.confirmDeleteLocation(); return; }
             if (e.target.closest('#backup-add-location-confirm')) { this.confirmAddLocation(); return; }
             const engineBtn = e.target.closest('[data-action="open-engine-details"]');
             if (engineBtn) { this.openEngineDetailsModal(engineBtn); return; }
@@ -965,10 +966,25 @@ class BackupPage {
         await this.saveSection(`location-${idx}`);
     }
 
-    async deleteInlineLocation(idx) {
+    deleteInlineLocation(idx) {
         const loc = (this.locations?.locations || []).find(l => l.idx === idx);
         const name = loc?.name || `Location ${idx}`;
-        if (!confirm(`Delete location "${name}"?\n\nBackup data already stored at this location is not deleted — only LibrePortal's reference to it. The password file on disk also stays in place.`)) return;
+        const modal = document.getElementById('backup-delete-location-modal');
+        const body  = document.getElementById('backup-delete-location-modal-body');
+        if (!modal || !body) return;
+        body.innerHTML = `
+            <p>Delete location <strong>${this.escape(name)}</strong>?</p>
+            <p class="backup-card-hint">Backup data already stored at this location is not deleted — only LibrePortal's reference to it. The password file on disk also stays in place.</p>
+        `;
+        modal.dataset.locIdx = String(idx);
+        modal.classList.add('open');
+    }
+
+    async confirmDeleteLocation() {
+        const modal = document.getElementById('backup-delete-location-modal');
+        if (!modal) return;
+        const idx = parseInt(modal.dataset.locIdx, 10);
+        this.closeAllModals();
         this.expandedLocs.delete(idx);
         await this.runTask(`libreportal backup location remove ${idx}`, 'backup', null);
         setTimeout(() => this.reloadAfterSave(), 2000);