fix(auth): move initialAuthState/AuthState to auth-types.ts

Server-action files ('use server') can only export async functions.
Exporting initialAuthState (object) caused:
  'A use server file can only export async functions, found object'
when sign-up form was submitted.

Moved AuthState type and initialAuthState const to lib/appwrite/auth-types.ts.
Updated 3 form components to import the const from the new location.

src/lib/appwrite/auth-actions.ts

@@ -5,13 +5,7 @@ import { redirect } from "next/navigation";
 import { AppwriteException, ID } from "node-appwrite";
 
 import { APPWRITE_SESSION_COOKIE, createAdminClient, createSessionClient } from "./server";
-
-export type AuthState = {
-  ok: boolean;
-  error?: string;
-};
-
-const initial: AuthState = { ok: false };
+import type { AuthState } from "./auth-types";
 
 function appwriteError(e: unknown): string {
   if (e instanceof AppwriteException) {
@@ -114,5 +108,3 @@ export async function signOutAction() {
   (await cookies()).delete(APPWRITE_SESSION_COOKIE);
   redirect("/sign-in");
 }
-
-export const initialAuthState = initial;