feat: add database models with cascade delete

Implements SQLAlchemy 2.0 async ORM models (Config, Subscription, ExportLog) with cascade delete-orphan relationships. Upgrades SQLAlchemy to 2.0.49 for Python 3.14 compatibility. Adds pytest conftest with in-memory SQLite fixture; all 4 TDD tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/tests/test_models.py

@@ -0,0 +1,67 @@
+import uuid
+import pytest
+from sqlalchemy import select
+from models import Config, Subscription, ExportLog
+
+
+async def test_config_insert_and_retrieve(db_session):
+    token = str(uuid.uuid4())
+    config = Config(name="my-config", token=token, base_yaml="proxies: []")
+    db_session.add(config)
+    await db_session.commit()
+
+    result = await db_session.execute(select(Config).where(Config.token == token))
+    found = result.scalar_one()
+    assert found.id is not None
+    assert found.name == "my-config"
+    assert found.created_at is not None
+
+
+async def test_subscription_belongs_to_config(db_session):
+    config = Config(name="c", token=str(uuid.uuid4()), base_yaml="proxies: []")
+    db_session.add(config)
+    await db_session.flush()
+
+    sub = Subscription(config_id=config.id, name="provider1", url="https://example.com/sub")
+    db_session.add(sub)
+    await db_session.commit()
+
+    result = await db_session.execute(select(Subscription).where(Subscription.config_id == config.id))
+    subs = result.scalars().all()
+    assert len(subs) == 1
+    assert subs[0].name == "provider1"
+
+
+async def test_cascade_delete_removes_subscriptions(db_session):
+    config = Config(name="c", token=str(uuid.uuid4()), base_yaml="proxies: []")
+    db_session.add(config)
+    await db_session.flush()
+
+    sub = Subscription(config_id=config.id, name="p", url="https://example.com/sub")
+    log = ExportLog(config_id=config.id, node_count=5, success=True)
+    db_session.add(sub)
+    db_session.add(log)
+    await db_session.commit()
+
+    sub_id = sub.id
+    log_id = log.id
+
+    await db_session.delete(config)
+    await db_session.commit()
+
+    assert (await db_session.get(Subscription, sub_id)) is None
+    assert (await db_session.get(ExportLog, log_id)) is None
+
+
+async def test_export_log_defaults(db_session):
+    config = Config(name="c", token=str(uuid.uuid4()), base_yaml="proxies: []")
+    db_session.add(config)
+    await db_session.flush()
+
+    log = ExportLog(config_id=config.id)
+    db_session.add(log)
+    await db_session.commit()
+
+    assert log.success is True
+    assert log.node_count == 0
+    assert log.fetched_at is not None