Replace the deprecated via_device with via_device_id

Home Assistant 2026.9 deprecates the `via_device` (domain, identifier)
tuple in favour of `via_device_id`, which takes the parent device's
registry id; `via_device` stops working in 2027.8.0.

Register the hub device explicitly in async_setup_entry before the
platforms are forwarded, so the per-identity entities can look it up and
pass its `.id`. The hub device info moves into a shared helper so both
call sites describe the same device.

custom_components/reticulum/__init__.py

@@ -22,6 +22,7 @@ from homeassistant.core import (
 )
 from homeassistant.exceptions import ConfigEntryNotReady, HomeAssistantError
 from homeassistant.helpers import config_validation as cv
+from homeassistant.helpers import device_registry as dr
 from homeassistant.helpers.event import async_track_time_interval
 
 from .const import (
@@ -62,6 +63,7 @@ from .const import (
     STORAGE_SUBDIR,
     SUBENTRY_TYPE_IDENTITY,
 )
+from .entity import hub_device_info
 from .reticulum_client import (
     IdentityManager,
     ReticulumError,
@@ -130,6 +132,12 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
         )
         runtime.identities[subentry.subentry_id] = manager
 
+    # Register the hub device before the platforms, so the per-identity devices can
+    # link to it with `via_device_id`.
+    dr.async_get(hass).async_get_or_create(
+        config_entry_id=entry.entry_id, **hub_device_info(entry)
+    )
+
     await hass.config_entries.async_forward_entry_setups(entry, PLATFORMS)
 
     # Per-identity announce + periodic schedules.