Add API tokens and OAuth2 client support for external integrations

- Personal API tokens (model, user-settings UI, admin, management command,
  DRF auth class) for non-interactive API access from automations like n8n.
  Raw token shown once; only a SHA-256 hash is stored; last_used_at writes
  are throttled.
- OAuth2 authorization server via django-oauth-toolkit with authorization
  server metadata and optional, off-by-default Dynamic Client Registration
  (RFC 7591), so remote OAuth/MCP clients can authenticate and self-register.
- Tests for token auth, DCR gating and the management commands, plus
  .env.example and README documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/apps/users/migrations/0026_apitoken.py

@@ -0,0 +1,36 @@
+# Generated by Django 5.2.15 on 2026-06-24 09:21
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('users', '0025_alter_usersettings_default_account'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='APIToken',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=255, verbose_name='Name')),
+                ('token_key', models.CharField(db_index=True, max_length=16, unique=True, verbose_name='Token key')),
+                ('token_hash', models.CharField(max_length=255, verbose_name='Token hash')),
+                ('last_used_at', models.DateTimeField(blank=True, null=True, verbose_name='Last used at')),
+                ('expires_at', models.DateTimeField(blank=True, null=True, verbose_name='Expires at')),
+                ('revoked_at', models.DateTimeField(blank=True, null=True, verbose_name='Revoked at')),
+                ('created_at', models.DateTimeField(auto_now_add=True, verbose_name='Created at')),
+                ('updated_at', models.DateTimeField(auto_now=True, verbose_name='Updated at')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='api_tokens', to=settings.AUTH_USER_MODEL, verbose_name='User')),
+            ],
+            options={
+                'verbose_name': 'API token',
+                'verbose_name_plural': 'API tokens',
+                'ordering': ['-created_at'],
+                'indexes': [models.Index(fields=['user', 'revoked_at'], name='users_apito_user_id_73edec_idx'), models.Index(fields=['expires_at'], name='users_apito_expires_2b737c_idx')],
+            },
+        ),
+    ]