Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/ThemeToggle.tsx

@@ -0,0 +1,18 @@
+import { useT } from "../i18n";
+import { useTheme } from "../lib/theme";
+
+// Quick light/dark flip (the full light/dark/system selector lives in Settings).
+export function ThemeToggle() {
+  const t = useT();
+  const { resolved, setTheme } = useTheme();
+  return (
+    <button
+      className="rounded p-2 text-app-muted hover:bg-app-hover hover:text-app-fg"
+      title={t("theme.toggle")}
+      aria-label={t("theme.toggle")}
+      onClick={() => setTheme(resolved === "dark" ? "light" : "dark")}
+    >
+      {resolved === "dark" ? "☀" : "☾"}
+    </button>
+  );
+}