feat v1.12.0: Quality Scale conformance (phases 7-8)

- entry.runtime_data (HouseplanData in store.py) instead of hass.data; WS answers
  not_ready without a loaded entry
- test-before-setup (ConfigEntryNotReady), async_unload_entry, async_remove_entry
  (Lovelace resource cleanup), single_config_entry in manifest
- Store minor_version + migration hook; diagnostics.py (redacted); repairs
  (broken_plan issues, en/ru); system_health.py; strings.json
- quality_scale.yaml self-assessment; HA-harness tests (config flow, WS, upload)
  in CI on py3.13; CI backend job updated

.github/workflows/validate.yml

@@ -39,7 +39,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
-        with: { python-version: "3.12" }
-      - run: pip install pytest voluptuous
-      - name: Backend unit tests
+        with: { python-version: "3.13" }
+      - run: pip install pytest voluptuous pytest-homeassistant-custom-component
+      - name: Backend unit tests (pure + HA harness)
         run: python -m pytest tests_backend/ -q