i18n(web): full landing page TR↔EN — language switcher actually works now

Root cause: landing was almost entirely hard-coded Turkish (5 t() calls in
1889 lines), and initLocale() — which reads the persisted locale from
localStorage on boot — was never called from main.tsx, so a reload always
reverted to the TR default.

This commit fixes both.

apps/web/src/main.tsx
- Call initLocale() before first render so the persisted choice survives reload.

apps/web/src/routes/__root.tsx
- Translate the skip-to-content link via a new `a11y.skipToContent` key.

apps/web/src/routes/index.tsx
- Internationalize ~145 user-visible strings across hero, brand strip, features,
  comparison table, bento grid, use cases, stats, dashboard showcase, ecommerce
  block, testimonials, pricing tiers, FAQ, final CTA, referral banner and ARIA
  labels. Module-scope data arrays moved inside the component so re-renders
  pick up the active locale.
- Wrap the three Remotion players (Schema / Dashboard / Ecommerce) so they read
  the current locale and pass translated labels into their inputProps.

Remotion demos (DashboardDemo, EcommerceDemo, SchemaDemo)
- Each now accepts a `labels` prop (DashboardDemoLabels / EcommerceDemoLabels /
  partLabel). All hard-coded TR sidebar items, placeholders, category names,
  product names, "Add to Cart" buttons, the cart-added toast, overlays and
  stat labels are now driven by labels with a TR fallback (keeps Remotion
  Studio preview working standalone).

messages/{tr,en}.json
- New blocks: `a11y`, `landing.*` (huge tree covering every section above),
  `landing.dashboardDemo`, `landing.ecommerceDemo`.

Intentionally preserved as data, not translated: brand names (Volkswagen,
Mitsubishi …), VIN literals, OEM codes (1J0 820 803F …), numeric stat values
(1.2sn, 27, 1M+, %99.9 …), prices (200/350/500/999), and the testimonial
person name "Özge D." (proper noun).

Verified: typecheck clean, 17/17 test files / 57/57 tests pass, biome clean,
Playwright TR↔EN round-trip succeeds, only the testimonial name remains as
Turkish on the EN page.

apps/web/src/routes/__root.tsx

@@ -1,6 +1,7 @@
 import { useAuth } from "@/hooks/use-auth";
 import { api } from "@/lib/api-client";
 import { resetChatwootUser, setChatwootUser } from "@/lib/chatwoot";
+import { useTranslation } from "@/lib/i18n";
 import { trackPageView as trackMetaPageView } from "@/lib/meta-pixel";
 import { capturePageView, identifyUser, resetUser } from "@/lib/posthog";
 import { Toaster } from "@/lib/toast";
@@ -92,6 +93,7 @@ function applyTheme(theme: "light" | "dark" | "system") {
 function RootComponent() {
   const location = useLocation();
   const { user } = useAuth();
+  const { t } = useTranslation();
 
   // Pageview tracking
   useEffect(() => {
@@ -135,7 +137,7 @@ function RootComponent() {
   return (
     <>
       <a href="#main-content" className="skip-link">
-        İçeriğe atla
+        {t("a11y.skipToContent")}
       </a>
       <Outlet />
       <Toaster position="top-center" />