feat: implement user authentication with login and register

- Add login screen with email/username support
- Add register screen with email validation
- Implement AuthStore with expo-secure-store (native) / localStorage (web)
- Add X-User-Id header authentication (simple auth without JWT)
- Rename displayName to userName across codebase
- Add findByUserName() to UserRepository
- Check for existing email AND username on registration
- Add AuthButton component with shadow effect
- Add logout button to Header
- Add hash-password.js utility script for manual password resets
- Update CORS to allow X-User-Id header

apps/server/src/services/AuthService.ts

@@ -7,7 +7,12 @@ export class AuthService {
   constructor(private userRepo: UserRepository) {}
 
   async login(data: LoginDTO): Promise<AuthResponse> {
-    const user = await this.userRepo.findByEmail(data.email);
+    // Try email first, then userName
+    let user = await this.userRepo.findByEmail(data.identifier);
+    if (!user) {
+      user = await this.userRepo.findByUserName(data.identifier);
+    }
+
     if (!user || !user.passwordHash) {
       throw new Error("Invalid credentials");
     }
@@ -21,15 +26,20 @@ export class AuthService {
   }
 
   async register(data: CreateUserDTO): Promise<AuthResponse> {
-    const existingUser = await this.userRepo.findByEmail(data.email);
-    if (existingUser) {
+    const existingEmail = await this.userRepo.findByEmail(data.email);
+    if (existingEmail) {
       throw new Error("Email already exists");
     }
 
+    const existingUserName = await this.userRepo.findByUserName(data.userName);
+    if (existingUserName) {
+      throw new Error("Username already exists");
+    }
+
     const passwordHash = await password.hash(data.password);
     const user = await this.userRepo.create({
       email: data.email,
-      displayName: data.displayName,
+      userName: data.userName,
       passwordHash,
     });
 

apps/server/src/services/interfaces/UserRepository.ts

@@ -2,12 +2,13 @@ import { User } from "@caldav/shared";
 
 export interface CreateUserData {
   email: string;
-  displayName: string;
+  userName: string;
   passwordHash: string;
 }
 
 export interface UserRepository {
   findById(id: string): Promise<User | null>;
   findByEmail(email: string): Promise<User | null>;
+  findByUserName(userName: string): Promise<User | null>;
   create(data: CreateUserData): Promise<User>;
 }