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

custom_components/houseplan/strings.json

@@ -0,0 +1,24 @@
+{
+  "config": {
+    "step": {
+      "user": {
+        "title": "House Plan",
+        "data": { "admin_only": "Only administrators may edit the layout" }
+      }
+    },
+    "abort": { "single_instance_allowed": "Already configured — only one entry is allowed." }
+  },
+  "options": {
+    "step": {
+      "init": {
+        "data": { "admin_only": "Only administrators may edit the layout" }
+      }
+    }
+  },
+  "issues": {
+    "broken_plan": {
+      "title": "Floor plan image is missing",
+      "description": "The plan file `{file}` for space `{space}` was not found in `config/houseplan/plans/`. Open the space settings in the House Plan card and upload the plan again."
+    }
+  }
+}