M6-T01: add 5 energy tables, models, and migration

- app/models/energy.py: DsmrReading, EnergyContract, EnergyContractVersion,
  TibberPrice, EnergyCostPeriod (per design §3.5; JSON blobs, RESTRICT FKs).
- alembic_app migration 20260623_11_energy_tables (head), env.py imports.
- app_db_adopt APP_BASELINE_REVISION bumped to new head.
- tests/test_energy_models.py + expose_catalog test fixups for new head.

tests/test_expose_catalog.py

@@ -530,7 +530,13 @@ def test_exposed_entity_toggle_key_unique_index(expose_db):
 
 
 def test_downgrade_removes_toggle_table(tmp_path: Path):
-    """downgrade -1 from head must drop the exposed_entity_toggle table cleanly."""
+    """Downgrading to the revision before exposed_entity_toggle must drop that table cleanly.
+
+    We downgrade to the explicit down_revision of the expose-toggle migration
+    (``20260622_09_modbus_tables``) rather than using ``-1`` from head, so the test
+    remains correct as new revisions are added on top.  This is the same pattern
+    used in test_modbus_models.py for the modbus downgrade test.
+    """
     db_path = tmp_path / "downgrade_expose_test.db"
     db_url = f"sqlite:///{db_path}"
     alembic_cfg = _make_app_alembic_config(db_url)
@@ -542,14 +548,15 @@ def test_downgrade_removes_toggle_table(tmp_path: Path):
     assert "exposed_entity_toggle" in inspector.get_table_names()
     engine.dispose()
 
-    # Downgrade one step removes the exposed_entity_toggle revision.
-    command.downgrade(alembic_cfg, "-1")
+    # Downgrade to the explicit down_revision of the exposed_entity_toggle migration,
+    # consistent with how test_modbus_models.py handles its own downgrade test.
+    command.downgrade(alembic_cfg, "20260622_09_modbus_tables")
 
     engine = create_engine(db_url, connect_args={"check_same_thread": False})
     inspector = inspect(engine)
     table_names = inspector.get_table_names()
     assert "exposed_entity_toggle" not in table_names, (
-        "exposed_entity_toggle should be gone after downgrade -1"
+        "exposed_entity_toggle should be gone after downgrade to 20260622_09_modbus_tables"
     )
     # Previous tables must still exist.
     assert "modbus_device" in table_names
@@ -668,7 +675,7 @@ def test_expose_toggle_update(expose_db):
 
 
 def test_app_baseline_revision_matches_new_head(tmp_path: Path):
-    """APP_BASELINE_REVISION must equal the Alembic head after the new migration."""
+    """APP_BASELINE_REVISION must equal the Alembic head revision."""
     from alembic.script import ScriptDirectory
 
     from scripts.app_db_adopt import APP_BASELINE_REVISION
@@ -683,7 +690,3 @@ def test_app_baseline_revision_matches_new_head(tmp_path: Path):
         f"APP_BASELINE_REVISION={APP_BASELINE_REVISION!r} does not match "
         f"Alembic head={head!r}"
     )
-    # Confirm the new revision is the head.
-    assert head == "20260622_10_exposed_entities", (
-        f"Expected new head to be '20260622_10_exposed_entities', got {head!r}"
-    )