Rename gas cooktop registry's display name to avoid induction_cooktop confusion

Renames DeviceRegistry.name from 'cooktop' to 'gas_cooktop' for the
NA9300K-class gas-cooktop registry (PR #23), so diagnostics/device-info
labels no longer collide with the unrelated induction_cooktop family
(issue #86) -- two different OCF surfaces that happen to share the
English word "cooktop".

Safe rename: _REGISTRY_BY_KEY's 'cooktop' lookup key is unchanged, so
all three existing detection paths (oneUiVersion "Cooktop" exact
match, the legacy ARTIK051 modelNum rule, and the resource-signature
fallback) keep routing real devices exactly as before. Entity
unique_ids are built from device serial + entity key, not registry
name, so existing entities are unaffected. Only the DeviceInfo.name
and diagnostics device_type strings change, both cosmetic.

tests/localthings/test_coordinator.py

@@ -169,7 +169,7 @@ def test_run_discovery_detects_cooktop_via_resource_signature(
     coordinator = LocalThingsCoordinator(hass, mock_entry)
     coordinator._run_discovery(_load_device('cooktop'))
 
-    assert coordinator.device_type_name == 'cooktop'
+    assert coordinator.device_type_name == 'gas_cooktop'
     assert coordinator._unbound_hrefs == []
 
 

tests/test_by_type.py

@@ -42,9 +42,12 @@ class TestForDevice:
         assert registry.name == 'refrigerator'
 
     def test_for_device_returns_cooktop_registry(self):
+        """The registry's own .name is 'gas_cooktop' (disambiguated from
+        induction_cooktop), but the lookup key devices route through stays
+        'cooktop' -- oneUiVersion "Cooktop" still resolves here."""
         registry = for_device('7.0 Cooktop')
         assert registry is not None
-        assert registry.name == 'cooktop'
+        assert registry.name == 'gas_cooktop'
 
     def test_for_device_returns_range_hood_registry(self):
         registry = for_device('7.0 Range Hood')
@@ -258,7 +261,7 @@ class TestForDeviceByModel:
             'ARTIK051_GLOBAL_COOKTOP',
         )
         assert reg is not None
-        assert reg.name == 'cooktop'
+        assert reg.name == 'gas_cooktop'
 
     def test_range_hood_via_ahd_model(self):
         from custom_components.localthings.registry.by_type import for_device_by_model
@@ -319,7 +322,7 @@ class TestForDeviceByResources:
         reg = for_device_by_resources(_load_device('cooktop'))
 
         assert reg is not None
-        assert reg.name == 'cooktop'
+        assert reg.name == 'gas_cooktop'
 
     def test_unrelated_mode_options_are_not_cooktop(self):
         from custom_components.localthings.registry.by_type import for_device_by_resources