add Session entity, persistence, fake

Session: immutable holder of token, owning User, createdAt,
expiresAt. isExpired(now) compares >= expiresAt. SessionModel
keys on token (string primary, non-incrementing). migration adds
sessions table with foreign user_id (cascade on user delete) and
indexed expires_at for cleanup queries. EloquentSessionRepository
takes UserRepository to rehydrate the owning User on findByToken;
sessions for deleted users return null. FakeSessionRepository
mirrors with an in-memory map keyed by token, defensive copies on
read.

backend/app/Auth/CreateSessionDto.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace App\Auth;
+
+use App\User\User;
+use DateTimeImmutable;
+
+class CreateSessionDto
+{
+    public function __construct(
+        public string $token,
+        public User $user,
+        public DateTimeImmutable $createdAt,
+        public DateTimeImmutable $expiresAt,
+    ) {}
+}

backend/app/Auth/EloquentSessionRepository.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace App\Auth;
+
+use App\User\UserRepository;
+use DateTimeImmutable;
+use DateTimeZone;
+
+class EloquentSessionRepository implements SessionRepository
+{
+    public function __construct(private UserRepository $userRepo) {}
+
+    public function create(CreateSessionDto $dto): Session
+    {
+        SessionModel::create([
+            'token' => $dto->token,
+            'user_id' => $dto->user->getId(),
+            'created_at' => $dto->createdAt,
+            'expires_at' => $dto->expiresAt,
+        ]);
+
+        return new Session(
+            token: $dto->token,
+            user: $dto->user,
+            createdAt: $dto->createdAt,
+            expiresAt: $dto->expiresAt,
+        );
+    }
+
+    public function findByToken(string $token): ?Session
+    {
+        $model = SessionModel::find($token);
+        if ($model === null) {
+            return null;
+        }
+        $user = $this->userRepo->find($model->user_id);
+        if ($user === null) {
+            return null;
+        }
+        $utc = new DateTimeZone('UTC');
+
+        return new Session(
+            token: $model->token,
+            user: $user,
+            createdAt: new DateTimeImmutable(
+                $model->created_at->toDateTimeString(),
+                $utc
+            ),
+            expiresAt: new DateTimeImmutable(
+                $model->expires_at->toDateTimeString(),
+                $utc
+            ),
+        );
+    }
+
+    public function deleteByToken(string $token): void
+    {
+        SessionModel::where('token', $token)->delete();
+    }
+}

backend/app/Auth/Session.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace App\Auth;
+
+use App\User\User;
+use DateTimeImmutable;
+
+class Session
+{
+    public function __construct(
+        private string $token,
+        private User $user,
+        private DateTimeImmutable $createdAt,
+        private DateTimeImmutable $expiresAt,
+    ) {}
+
+    public function getToken(): string
+    {
+        return $this->token;
+    }
+
+    public function getUser(): User
+    {
+        return $this->user;
+    }
+
+    public function getCreatedAt(): DateTimeImmutable
+    {
+        return $this->createdAt;
+    }
+
+    public function getExpiresAt(): DateTimeImmutable
+    {
+        return $this->expiresAt;
+    }
+
+    public function isExpired(DateTimeImmutable $now): bool
+    {
+        return $now >= $this->expiresAt;
+    }
+}

backend/app/Auth/SessionModel.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace App\Auth;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Carbon;
+
+/**
+ * @property string $token
+ * @property int $user_id
+ * @property Carbon $created_at
+ * @property Carbon $expires_at
+ *
+ * @method static Builder<static>|SessionModel newModelQuery()
+ * @method static Builder<static>|SessionModel newQuery()
+ * @method static Builder<static>|SessionModel query()
+ *
+ * @mixin \Eloquent
+ */
+class SessionModel extends Model
+{
+    protected $table = 'sessions';
+
+    protected $primaryKey = 'token';
+
+    public $incrementing = false;
+
+    protected $keyType = 'string';
+
+    public $timestamps = false;
+
+    protected $fillable = [
+        'token',
+        'user_id',
+        'created_at',
+        'expires_at',
+    ];
+
+    protected $casts = [
+        'created_at' => 'datetime',
+        'expires_at' => 'datetime',
+    ];
+}

backend/app/Auth/SessionRepository.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Auth;
+
+interface SessionRepository
+{
+    public function create(CreateSessionDto $dto): Session;
+
+    public function findByToken(string $token): ?Session;
+
+    public function deleteByToken(string $token): void;
+}