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/stores/instanceStore.ts

@@ -91,6 +91,7 @@ interface InstanceState {
   connectToRemote: (origin: string, password: string, displayName?: string) => Promise<void>;
   loginToRemote: (origin: string, username: string, password: string) => Promise<void>;
   removeInstance: (origin: string) => void;
+  setInstanceStatus: (origin: string, status: ConnectedInstance['status'], error?: string) => void;
   syncInstanceList: () => Promise<void>;
   autoConnectAll: () => Promise<void>;
   reset: () => void;
@@ -276,6 +277,14 @@ export const useInstanceStore = create<InstanceState>((set, get) => ({
     }
   },
 
+  setInstanceStatus: (origin, status, error) => {
+    set((state) => ({
+      instances: state.instances.map(i =>
+        i.origin === origin ? { ...i, status, error } : i
+      ),
+    }));
+  },
+
   removeInstance: (origin: string) => {
     // Tear down WebSocket connection
     disconnectInstance(origin);