refactor(tests): compress admin_client + mock_send_email into conftest

Lift admin_client fixture from 7 duplicate definitions into conftest.py.
Add mock_send_email fixture, replacing 60 inline patch() blocks across
test_emails.py, test_waitlist.py, and test_businessplan.py. Net -197 lines.

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

web/tests/conftest.py

@@ -125,6 +125,32 @@ async def auth_client(app, test_user):
         yield c
 
 
+@pytest.fixture
+async def admin_client(app, db):
+    """Test client with an admin user pre-loaded in session."""
+    now = datetime.now(UTC).isoformat()
+    async with db.execute(
+        "INSERT INTO users (email, name, created_at) VALUES (?, ?, ?)",
+        ("admin@test.com", "Admin", now),
+    ) as cursor:
+        user_id = cursor.lastrowid
+    await db.execute(
+        "INSERT INTO user_roles (user_id, role) VALUES (?, 'admin')", (user_id,)
+    )
+    await db.commit()
+    async with app.test_client() as c:
+        async with c.session_transaction() as sess:
+            sess["user_id"] = user_id
+        yield c
+
+
+@pytest.fixture
+def mock_send_email():
+    """Patch padelnomics.worker.send_email for the duration of the test."""
+    with patch("padelnomics.worker.send_email", new_callable=AsyncMock) as mock:
+        yield mock
+
+
 # ── Subscriptions ────────────────────────────────────────────
 
 @pytest.fixture