feat: stateless federated identity resolver + federation UX improvements

Add identity.ts with isSelf() and resolveDisplayIdentity() — pure
stateless functions that detect replicated-self using the immutable
(username, homeInstance) composite key. No store lookups, no data
mutation. Fixes wrong avatar gradient and missing edit/delete on
own messages in remote channels.

Also includes: optimistic message dedup fix for cross-instance
messages (content-only matching), federation toast notifications,
Username component with @domain display, invite parser, and
deploy script simplification.

packages/web/src/components/ui/ToastContainer.tsx

@@ -0,0 +1,29 @@
+import React from 'react';
+import { useUIStore } from '../../stores/uiStore';
+
+const borderColors = {
+  info: 'border-l-accent-sky',
+  warning: 'border-l-accent-amber',
+  success: 'border-l-accent-mint',
+} as const;
+
+export function ToastContainer() {
+  const toasts = useUIStore((s) => s.toasts);
+  const removeToast = useUIStore((s) => s.removeToast);
+
+  if (toasts.length === 0) return null;
+
+  return (
+    <div className="fixed bottom-6 right-6 z-[300] flex flex-col gap-2 pointer-events-none">
+      {toasts.map((toast) => (
+        <div
+          key={toast.id}
+          className={`glass-pill border-l-2 ${borderColors[toast.type]} rounded-[10px] px-4 py-2.5 max-w-[320px] animate-slide-up pointer-events-auto cursor-pointer`}
+          onClick={() => removeToast(toast.id)}
+        >
+          <span className="text-sm text-txt-primary leading-snug">{toast.message}</span>
+        </div>
+      ))}
+    </div>
+  );
+}