Introduce SWSRuntimeData dataclass for typed entry.runtime_data.

Adds the SWSRuntimeData dataclass and SWSConfigEntry type alias so
  per-entry state can move from loosely-typed hass.data[DOMAIN][entry_id]
  dicts to HA 2025+ typed entry.runtime_data. The legacy ENTRY_* string
  keys are kept in place for now so callers can be migrated incrementally.

  This commit is not final update. Just preparing for future complete refactor.

custom_components/sws12500/data.py

@@ -1,16 +1,54 @@
-"""Shared keys for storing integration runtime state in `hass.data`.
+"""Shared keys for storing integration runtime data.
 
-This integration stores runtime state under:
+HA 2025+ pattern: structured runtime state stored in entry.runtime_data
-
+instead of loosely-typed hass.data[][] dicts.
-    hass.data[DOMAIN][entry_id]  -> dict
-
-Keeping keys in a dedicated module prevents subtle bugs where different modules
-store different types under the same key.
 """
 
 from __future__ import annotations
 
-from typing import Final
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Any
+
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core_config import Config
+from homeassistant.exceptions import NoEntitySpecifiedError
+from homeassistant.helpers.entity_platform import AddEntitiesCallback
+
+if TYPE_CHECKING:
+    from . import WeatherDataUpdateCoordinator
+    from .ecowitt import EcowittBridge
+    from .health_coordinator import HealthCoordinator
+    from .sensors_common import WeatherSensorEntityDescription
+
+
+@dataclass
+class SWSRuntimeData:
+    """Per-entry runtime state for SWS12500 integration.
+
+    Stored in entry.runtime_data. Type-safe, no string key lookups,
+    no checked() boilerplate
+    """
+
+    # Core coordinators
+    coordinator: WeatherDataUpdateCoordinator
+    health_coordinator: HealthCoordinator
+
+    # Sensor platform callbacks (set by sensor.async_setup_entry)
+    add_sensor_entities: AddEntitiesCallback | None = None
+    sensor_descriptions: dict[str, WeatherSensorEntityDescription] | None = None
+
+    # Binary sensor platform callbacks
+    add_binary_entities: AddEntitiesCallback | None = None
+    binary_description: dict[str, Any] | None = None
+    added_binary_keys: set[str] = field(default_factory=dict)
+
+    # Health data cache for diagnostics
+    health_data: dict[str, Any] | None = None
+
+
+# Type alias for typed ConfigEntry
+type SWSConfigEntry = ConfigEntry[SWSRuntimeData]
+
 
 # Per-entry dict keys stored under hass.data[DOMAIN][entry_id]
 ENTRY_COORDINATOR: Final[str] = "coordinator"