feat: Phase 1 Group 7 — add account_id to script tables (keep team_id)

team_id is kept in all three tables — drop deferred until app code
is fully migrated off team_id references.

Tables: script_builder_sessions, script_templates, script_generations
Backfill: user_id/created_by → users.account_id

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

backend/tests/test_phase1_migrations.py

@@ -420,3 +420,26 @@ async def test_maintenance_schedule_account_id_matches_tree(test_db: AsyncSessio
     )
     row = result.scalar_one()
     assert row.account_id == account.id
+
+
+# ── Group 7: Legacy team_id tables ───────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_script_builder_session_account_id(test_db: AsyncSession):
+    """script_builder_sessions.account_id must match user's account_id."""
+    from app.models.script_builder_session import ScriptBuilderSession
+
+    account, user = await _make_account_and_user(test_db, "sbs1")
+    sbs = ScriptBuilderSession(
+        user_id=user.id,
+        account_id=account.id,
+        language="powershell",
+    )
+    test_db.add(sbs)
+    await test_db.commit()
+
+    result = await test_db.execute(
+        select(ScriptBuilderSession).where(ScriptBuilderSession.id == sbs.id)
+    )
+    row = result.scalar_one()
+    assert row.account_id == account.id