feat: Phase 1 Group 8 — add account_id to target_lists (keep team_id)

Zero rows in production — this is a schema-only migration in practice.
team_id kept for app code compatibility. Drop deferred to later cleanup.
Backfill: team_id → team admin user → account_id; fallback: created_by.

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

backend/tests/test_phase1_migrations.py

@@ -443,3 +443,38 @@ async def test_script_builder_session_account_id(test_db: AsyncSession):
     )
     row = result.scalar_one()
     assert row.account_id == account.id
+
+
+# ── Group 8: TargetList ────────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_target_list_account_id_from_team_admin(test_db: AsyncSession):
+    """target_lists.account_id must be set to the team admin's account_id."""
+    from app.models.target_list import TargetList
+    from app.models.team import Team
+
+    account, user = await _make_account_and_user(test_db, "tl1")
+    # Make user a team admin
+    team = Team(name=f"Team {uuid.uuid4().hex[:6]}")
+    test_db.add(team)
+    await test_db.flush()
+
+    user.team_id = team.id
+    user.is_team_admin = True
+    await test_db.flush()
+
+    target_list = TargetList(
+        team_id=team.id,
+        account_id=account.id,
+        created_by=user.id,
+        name="Server Targets",
+        targets=[{"label": "SRV-01"}],
+    )
+    test_db.add(target_list)
+    await test_db.commit()
+
+    result = await test_db.execute(
+        select(TargetList).where(TargetList.id == target_list.id)
+    )
+    row = result.scalar_one()
+    assert row.account_id == account.id