fix(buyer/billing/comms/a11y): Codex review pass round 2

Tuxedo buyer path (subagent 2):
- src/app/tuxedo/page.tsx: remove duplicate CinematicShowcase render
- src/components/storefront/CinematicShowcase.tsx: wire up useCart, Add to Cart button, brand-aware fulfillment
- src/app/tuxedo/stops/TuxedoStopsList.tsx: improved empty state with calendar icon + CTAs
- src/app/cart/CartClient.tsx: guard against empty cart checkout; 'Cart is Empty' state

Billing reconciliation (subagent 3):
- src/actions/billing/billing-overview.ts: NEW — single source of truth
- src/app/admin/settings/billing/page.tsx: use getBillingOverview
- src/app/admin/settings/billing/BillingClientPage.tsx: rewritten to consume BillingOverview (status pill, addons state, removable flags, derived invoice amounts, usage footer)
- src/app/admin/page.tsx: use getBillingOverview (aligns dashboard with billing)
- src/components/admin/DashboardClient.tsx: 'Active Products' now reads from getBillingOverview
- supabase/migrations/203_plan_usage_active_products.sql: get_brand_plan_info counts products as active=true AND deleted_at IS NULL

Harvest Reach dedup + audience preview (manual, subagent 4 didn't complete):
- src/components/admin/CommunicationsPage.tsx: add initialTab prop
- src/app/admin/communications/compose/page.tsx: now renders with initialTab='compose' (single compose experience, no duplicate edit panel)
- src/components/admin/HarvestReach/CampaignComposerPage.tsx: always-visible audience preview panel (count + sample emails), loads via previewCampaignAudience action

Layout/content consistency + a11y sweep (subagent 5):
- src/components/layout/SiteHeader.tsx: Admin link only shows for authenticated admin users
- src/components/Providers.tsx: suppress public SiteHeader/Footer for /admin, /cart, /checkout, /wholesale, /water (fixes duplicate headers)
- src/app/contact/ContactClientPage.tsx: Phone/Email now use tel:/mailto: links; dynamic year
- src/app/blog/page.tsx, changelog, privacy-policy, roadmap, security, terms-and-conditions, waitlist: dynamic year
- src/app/admin/wholesale/WholesaleClient.tsx: proper htmlFor/id, type=email/tel, autoComplete
- src/app/admin/settings/ai/AIClient.tsx: proper htmlFor/id, required + aria-required
- src/app/admin/settings/integrations/IntegrationsClient.tsx: only mask secret fields; add required + aria-required + CredentialField.required type
- src/app/admin/water-log/headgates/HeadgatesManager.tsx: htmlFor/id, aria-required
- src/components/admin/CreateUserModal.tsx: htmlFor/id, required, aria-required, aria-describedby, autoComplete
- src/app/admin/me/AdminMeClient.tsx, products/import, sales/import, water-log/settings, login, brands, tuxedo: a11y polish (ids/required/aria)

src/app/cart/CartClient.tsx

@@ -100,11 +100,12 @@ export default function CartClient() {
   }, [cart, hasPickupItems, setSelectedStop]);
 
   const handleCheckoutClick = useCallback(() => {
+    if (cart.length === 0) return;
     if (stopBrandMismatch) { setSelectedStop(null); return; }
     if (hasStopPickupItems && !selectedStop) { setShowStopPicker(true); return; }
     if (incompatibleItems.length > 0) { return; }
     window.location.href = "/checkout";
-  }, [stopBrandMismatch, hasStopPickupItems, selectedStop, incompatibleItems]);
+  }, [cart.length, stopBrandMismatch, hasStopPickupItems, selectedStop, incompatibleItems]);
 
   return (
     <div className="min-h-screen relative">
@@ -384,17 +385,24 @@ export default function CartClient() {
 
               <button
                 onClick={handleCheckoutClick}
-                disabled={hasStopPickupItems && (!selectedStop || incompatibleItems.length > 0)}
+                disabled={
+                  cart.length === 0 ||
+                  (hasStopPickupItems && (!selectedStop || incompatibleItems.length > 0))
+                }
                 className="mt-6 w-full rounded-xl bg-gradient-to-r from-emerald-500 to-emerald-400 hover:from-emerald-400 hover:to-emerald-300 px-6 py-3.5 text-base font-semibold text-white disabled:opacity-50 disabled:cursor-not-allowed transition-all shadow-lg shadow-emerald-500/20 hover:-translate-y-0.5"
                 aria-label={
-                  incompatibleItems.length > 0
+                  cart.length === 0
+                    ? "Your cart is empty. Add a product to continue."
+                    : incompatibleItems.length > 0
                     ? "Remove incompatible items first to proceed to checkout"
                     : !selectedStop && hasStopPickupItems
                     ? "Select pickup stop first to proceed to checkout"
                     : "Continue to checkout"
                 }
               >
-                {incompatibleItems.length > 0
+                {cart.length === 0
+                  ? "Cart is Empty"
+                  : incompatibleItems.length > 0
                   ? "Remove Incompatible Items First"
                   : !selectedStop && hasStopPickupItems
                   ? "Select Pickup Stop First"