feat(web): language switcher in dashboard header + shared component

Extract the footer's TR/EN toggle into a reusable LanguageSwitcher with
two variants: `inline` (segmented row, used by the footer) and
`dropdown` (round Globe icon + menu with active check). Add the dropdown
variant to the dashboard header next to the theme toggle so app users
can switch language without the marketing footer.

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

apps/web/src/routes/dashboard.tsx

@@ -1,3 +1,4 @@
+import { LanguageSwitcher } from "@/components/language-switcher";
 import { SiteFooter } from "@/components/site-footer";
 import { TrialUrgencyBanner } from "@/components/trial-urgency-banner";
 import { useAuth } from "@/hooks/use-auth";
@@ -493,6 +494,7 @@ function DashboardLayout() {
                   </Button>
                 </Link>
               )}
+              <LanguageSwitcher variant="dropdown" />
               <button
                 type="button"
                 onClick={toggleTheme}