Phone: the side panel takes the full screen width

The Calendar / Contacts / conversation side panel on a phone filled 88% of the
width (at most 420px); it now covers the whole screen, still sliding in from
the right.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/routes/MailLayout.tsx

@@ -1724,7 +1724,7 @@ export function MailLayout() {
           />
           <div
             aria-hidden={!sheetOpen}
-            className={`fixed inset-y-0 right-0 z-50 w-[88vw] max-w-[420px] border-l border-app-border pb-[env(safe-area-inset-bottom)] pt-[env(safe-area-inset-top)] shadow-2xl transition-transform duration-200 ease-out bg-app-surface ${
+            className={`fixed inset-y-0 right-0 z-50 w-full pb-[env(safe-area-inset-bottom)] pt-[env(safe-area-inset-top)] shadow-2xl transition-transform duration-200 ease-out bg-app-surface ${
               sheetOpen ? "translate-x-0" : "pointer-events-none translate-x-full"
             }`}
           >