fix: pure Python keypair generation, no wg CLI dependency

Replace subprocess calls to wg genkey/pubkey with cryptography
library's X25519PrivateKey. This eliminates the wg CLI dependency
for key generation, fixes device creation on machines without
wireguard-tools, and removes the event loop blocking that caused
WebSocket disconnects during device creation.

Also fix E2E test teardown to use a fresh engine for cleanup,
avoiding cross-event-loop issues with asyncpg connection pools.

tests/e2e/conftest.py

@@ -1,9 +1,12 @@
 """E2E test configuration — loads NiceGUI testing plugin and app."""
 
 import pytest
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import create_async_engine
 from sqlmodel import select
 
 from wiregui.auth.passwords import hash_password
+from wiregui.config import get_settings
 from wiregui.db import async_session
 from wiregui.models.configuration import Configuration
 from wiregui.models.user import User
@@ -14,24 +17,32 @@ FAKE_SERVER_KEY = "SFake0ServerPubKey0000000000000000000000000w="
 TEST_EMAIL = "e2e-test@example.com"
 TEST_PASSWORD = "testpass123"
 
-async def _delete_user_cascade(session, user_id):
-    """Delete a user and all related objects via raw SQL to avoid stale ORM cache issues."""
-    from sqlalchemy import text
-    for table in ("devices", "rules", "mfa_methods", "api_tokens", "oidc_connections"):
-        await session.execute(text(f"DELETE FROM {table} WHERE user_id = :uid"), {"uid": user_id})  # noqa: S608
-    await session.execute(text("DELETE FROM users WHERE id = :uid"), {"uid": user_id})
+_CHILD_TABLES = ("devices", "rules", "mfa_methods", "api_tokens", "oidc_connections")
+
+
+async def _cleanup_test_user():
+    """Delete the test user and all related objects using a fresh engine."""
+    engine = create_async_engine(get_settings().database_url)
+    async with engine.begin() as conn:
+        # Find user id by email
+        row = (await conn.execute(
+            text("SELECT id FROM users WHERE email = :email"), {"email": TEST_EMAIL}
+        )).first()
+        if row:
+            uid = row[0]
+            for table in _CHILD_TABLES:
+                await conn.execute(text(f"DELETE FROM {table} WHERE user_id = :uid"), {"uid": uid})  # noqa: S608
+            await conn.execute(text("DELETE FROM users WHERE id = :uid"), {"uid": uid})
+    await engine.dispose()
 
 
 @pytest.fixture
 async def test_user():
     """Create a test user and ensure server config has a public key."""
-    async with async_session() as session:
-        # Clean up any leftover from a previous failed run
-        existing = (await session.execute(select(User).where(User.email == TEST_EMAIL))).scalar_one_or_none()
-        if existing:
-            await _delete_user_cascade(session, existing.id)
-            await session.commit()
+    # Clean up any leftover from a previous failed run
+    await _cleanup_test_user()
 
+    async with async_session() as session:
         # Ensure a Configuration with a server key exists
         config = (await session.execute(select(Configuration).limit(1))).scalar_one_or_none()
         if config:
@@ -53,7 +64,4 @@ async def test_user():
 
     yield user
 
-    # Teardown
-    async with async_session() as session:
-        await _delete_user_cascade(session, user.id)
-        await session.commit()
+    await _cleanup_test_user()