Add COSS toast notifications and swap in the new logo

Wire COSS's (Base UI) Sonner-style stacked toast into the app:

- Install @coss/toast (components/ui/toast.tsx) and mount <ToastProvider> in
  the root layout; add a small notify.{success,error,info,warning} helper
  (lib/toast.ts) over toastManager so callers don't repeat the toast shape.
- Toast on the events requested: clinic created (onboarding), auth actions
  (sign in / sign up / sign out / password reset request + reset), patient
  saved (create/edit), and all failure branches as error toasts (kept inline
  errors as a fallback). New auth toast strings added to the en translation.
- Replace the logo everywhere: overwrite public/temetro-logo.png with the new
  1024² square mark (same aspect ratio as the old 500², so existing 32×32
  next/image usages stay undistorted; no reference changes needed).

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

frontend/app/(auth)/onboarding/page.tsx

@@ -7,6 +7,7 @@ import { AuthShell, Field, FormAlert } from "@/components/auth/auth-ui";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { authClient } from "@/lib/auth-client";
+import { notify } from "@/lib/toast";
 
 function slugify(value: string): string {
   return value
@@ -45,12 +46,15 @@ export default function OnboardingPage() {
     );
 
     if (createErr || !org) {
-      setError(createErr?.message ?? "Could not create the clinic.");
+      const message = createErr?.message ?? "Could not create the clinic.";
+      setError(message);
+      notify.error("Couldn't create clinic", message);
       setSubmitting(false);
       return;
     }
 
     await authClient.organization.setActive({ organizationId: org.id });
+    notify.success("Clinic created", `${org.name} is ready.`);
     router.push("/");
   };