a11y: scope=col + aria-label on storage stats table headers

The Storage card's per-streamer stats table was built without scope attributes on its <th> cells and the last column (the "Open" action column) had an empty header — screen readers couldn't tell which column a data cell belonged to once you tabbed into the rows, and the actions column had no announced name at all.

Fixes:
- All 6 column headers get scope="col" — explicit signal to screen readers that each <th> is a column header (the implicit <th>-inside-<thead> semantics work, but explicit scope is best practice for data tables and the de-facto standard for accessibility tooling validation)
- The empty actions header gets aria-label set from a new storageColumnActionsAria locale key (DE: "Aktionen", EN: "Actions") so screen readers announce "Aktionen, Spaltenkopf" for that column instead of skipping over an unnamed header.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/renderer-locale-de.ts

@@ -65,6 +65,7 @@ const UI_TEXT_DE = {
         storageColumnTotal: 'Gesamt',
         storageColumnLive: 'Live',
         storageColumnChat: 'Chat',
+        storageColumnActionsAria: 'Aktionen',
         storageOpen: 'Oeffnen',
         storageOtherFolders: 'Andere Ordner im Download-Pfad',
         cleanupTitle: 'Auto-Cleanup',

src/renderer-locale-en.ts

@@ -65,6 +65,7 @@ const UI_TEXT_EN = {
         storageColumnTotal: 'Total',
         storageColumnLive: 'Live',
         storageColumnChat: 'Chat',
+        storageColumnActionsAria: 'Actions',
         storageOpen: 'Open',
         storageOtherFolders: 'Other folders in download path',
         cleanupTitle: 'Auto-cleanup',

src/renderer-settings.ts

@@ -366,7 +366,12 @@ function renderStorageStats(stats: StorageStatsResult): void {
         ];
         for (const h of headers) {
             const th = document.createElement('th');
-            th.textContent = h;
+            th.scope = 'col';
+            if (h) {
+                th.textContent = h;
+            } else {
+                th.setAttribute('aria-label', UI_TEXT.static.storageColumnActionsAria);
+            }
             headRow.appendChild(th);
         }
         thead.appendChild(headRow);