feat(backend): Django + OpenCode 백엔드 추가 — 5_django_backend/

앱이 기대하는 base-backend 계약(envelope·JWT·/chat/stream SSE)을 그대로 구현.
Django 는 로그인·세션 미러(SQLite/PG)·OpenCode 이벤트 번역만 맡고, 답변은 전용
OpenCode 인스턴스(opencode/ workspace, codeassist 에이전트)가 만듦.
- accounts: 이메일 로그인, access 60분 / refresh 14일, entra/config 는 501
- chat: 세션 목록·검색·메시지·취소 + POST /chat/stream 어댑터(part.delta→token,
  idle→usage/done, 클라 끊겨도 턴 감시 태스크가 DB 마무리, 첫 이벤트 60초 타임아웃)
- OpenCode 1.18 멀티 프로젝트라 모든 요청에 ?directory= 부착
- docs-lib 에 OpenCode SDK 1.18.6 타입 원본, pytest 32

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

5_django_backend/apps/accounts/migrations/0001_initial.py

@@ -0,0 +1,145 @@
+# Generated by Django 5.1.15 on 2026-09-16 08:38
+
+import django.contrib.auth.models
+import django.contrib.auth.validators
+import django.utils.timezone
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ("auth", "0012_alter_user_first_name_max_length"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="User",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("password", models.CharField(max_length=128, verbose_name="password")),
+                (
+                    "last_login",
+                    models.DateTimeField(
+                        blank=True, null=True, verbose_name="last login"
+                    ),
+                ),
+                (
+                    "is_superuser",
+                    models.BooleanField(
+                        default=False,
+                        help_text="Designates that this user has all permissions without explicitly assigning them.",
+                        verbose_name="superuser status",
+                    ),
+                ),
+                (
+                    "username",
+                    models.CharField(
+                        error_messages={
+                            "unique": "A user with that username already exists."
+                        },
+                        help_text="Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.",
+                        max_length=150,
+                        unique=True,
+                        validators=[
+                            django.contrib.auth.validators.UnicodeUsernameValidator()
+                        ],
+                        verbose_name="username",
+                    ),
+                ),
+                (
+                    "first_name",
+                    models.CharField(
+                        blank=True, max_length=150, verbose_name="first name"
+                    ),
+                ),
+                (
+                    "last_name",
+                    models.CharField(
+                        blank=True, max_length=150, verbose_name="last name"
+                    ),
+                ),
+                (
+                    "is_staff",
+                    models.BooleanField(
+                        default=False,
+                        help_text="Designates whether the user can log into this admin site.",
+                        verbose_name="staff status",
+                    ),
+                ),
+                (
+                    "is_active",
+                    models.BooleanField(
+                        default=True,
+                        help_text="Designates whether this user should be treated as active. Unselect this instead of deleting accounts.",
+                        verbose_name="active",
+                    ),
+                ),
+                (
+                    "date_joined",
+                    models.DateTimeField(
+                        default=django.utils.timezone.now, verbose_name="date joined"
+                    ),
+                ),
+                (
+                    "email",
+                    models.EmailField(
+                        max_length=254, unique=True, verbose_name="이메일"
+                    ),
+                ),
+                (
+                    "user_name",
+                    models.CharField(
+                        blank=True, max_length=40, verbose_name="표시 이름"
+                    ),
+                ),
+                (
+                    "employee_id",
+                    models.CharField(blank=True, max_length=40, verbose_name="사번"),
+                ),
+                (
+                    "department",
+                    models.CharField(blank=True, max_length=80, verbose_name="부서"),
+                ),
+                (
+                    "groups",
+                    models.ManyToManyField(
+                        blank=True,
+                        help_text="The groups this user belongs to. A user will get all permissions granted to each of their groups.",
+                        related_name="user_set",
+                        related_query_name="user",
+                        to="auth.group",
+                        verbose_name="groups",
+                    ),
+                ),
+                (
+                    "user_permissions",
+                    models.ManyToManyField(
+                        blank=True,
+                        help_text="Specific permissions for this user.",
+                        related_name="user_set",
+                        related_query_name="user",
+                        to="auth.permission",
+                        verbose_name="user permissions",
+                    ),
+                ),
+            ],
+            options={
+                "verbose_name": "사용자",
+                "verbose_name_plural": "사용자",
+            },
+            managers=[
+                ("objects", django.contrib.auth.models.UserManager()),
+            ],
+        ),
+    ]