Use Docker's official registry domain detection logic (#6360)

* Use Docker's official registry domain detection logic

Replace the custom IMAGE_WITH_HOST regex with a proper implementation
based on Docker's reference parser (vendor/github.com/distribution/
reference/normalize.go).

Changes:
- Change DOCKER_HUB from "hub.docker.com" to "docker.io" (official default)
- Add DOCKER_HUB_LEGACY for backward compatibility with "hub.docker.com"
- Add IMAGE_DOMAIN_REGEX and get_domain() function that properly detects:
  - localhost (with optional port)
  - Domains with "." (e.g., ghcr.io, 127.0.0.1)
  - Domains with ":" port (e.g., myregistry:5000)
  - IPv6 addresses (e.g., [::1]:5000)
- Update credential handling to support both docker.io and hub.docker.com
- Add comprehensive tests for domain detection

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Refactor Docker domain detection to utils module

Move get_domain function to supervisor/docker/utils.py and rename it
to get_domain_from_image for consistency with get_registry_for_image.
Use named group in the regex for better readability.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Rename domain to registry for consistency

Use consistent "registry" terminology throughout the codebase:
- Rename get_domain_from_image to get_registry_from_image
- Rename IMAGE_DOMAIN_REGEX to IMAGE_REGISTRY_REGEX
- Update named group from "domain" to "registry"
- Update all related comments and variable names

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

tests/docker/test_credentials.py

@@ -1,9 +1,49 @@
 """Test docker login."""
 
+import pytest
+
 # pylint: disable=protected-access
 from supervisor.coresys import CoreSys
-from supervisor.docker.const import DOCKER_HUB
+from supervisor.docker.const import DOCKER_HUB, DOCKER_HUB_LEGACY
 from supervisor.docker.interface import DockerInterface
+from supervisor.docker.utils import get_registry_from_image
+
+
+@pytest.mark.parametrize(
+    ("image_ref", "expected_registry"),
+    [
+        # No registry - Docker Hub images
+        ("nginx", None),
+        ("nginx:latest", None),
+        ("library/nginx", None),
+        ("library/nginx:latest", None),
+        ("homeassistant/amd64-supervisor", None),
+        ("homeassistant/amd64-supervisor:1.2.3", None),
+        # Registry with dot
+        ("ghcr.io/homeassistant/amd64-supervisor", "ghcr.io"),
+        ("ghcr.io/homeassistant/amd64-supervisor:latest", "ghcr.io"),
+        ("myregistry.com/nginx", "myregistry.com"),
+        ("registry.example.com/org/image:v1", "registry.example.com"),
+        ("127.0.0.1/myimage", "127.0.0.1"),
+        # Registry with port
+        ("myregistry:5000/myimage", "myregistry:5000"),
+        ("localhost:5000/myimage", "localhost:5000"),
+        ("registry.io:5000/org/app:v1", "registry.io:5000"),
+        # localhost special case
+        ("localhost/myimage", "localhost"),
+        ("localhost/myimage:tag", "localhost"),
+        # IPv6
+        ("[::1]:5000/myimage", "[::1]:5000"),
+        ("[2001:db8::1]:5000/myimage:tag", "[2001:db8::1]:5000"),
+    ],
+)
+def test_get_registry_from_image(image_ref: str, expected_registry: str | None):
+    """Test get_registry_from_image extracts registry from image reference.
+
+    Based on Docker's reference implementation:
+    vendor/github.com/distribution/reference/normalize.go
+    """
+    assert get_registry_from_image(image_ref) == expected_registry
 
 
 def test_no_credentials(coresys: CoreSys, test_docker_interface: DockerInterface):
@@ -47,3 +87,36 @@ def test_matching_credentials(coresys: CoreSys, test_docker_interface: DockerInt
     )
     assert credentials["username"] == "Spongebob Squarepants"
     assert "registry" not in credentials
+
+
+def test_legacy_docker_hub_credentials(
+    coresys: CoreSys, test_docker_interface: DockerInterface
+):
+    """Test legacy hub.docker.com credentials are used for Docker Hub images."""
+    coresys.docker.config._data["registries"] = {
+        DOCKER_HUB_LEGACY: {"username": "LegacyUser", "password": "Password1!"},
+    }
+
+    credentials = test_docker_interface._get_credentials(
+        "homeassistant/amd64-supervisor"
+    )
+    assert credentials["username"] == "LegacyUser"
+    # No registry should be included for Docker Hub
+    assert "registry" not in credentials
+
+
+def test_docker_hub_preferred_over_legacy(
+    coresys: CoreSys, test_docker_interface: DockerInterface
+):
+    """Test docker.io is preferred over legacy hub.docker.com when both exist."""
+    coresys.docker.config._data["registries"] = {
+        DOCKER_HUB: {"username": "NewUser", "password": "Password1!"},
+        DOCKER_HUB_LEGACY: {"username": "LegacyUser", "password": "Password2!"},
+    }
+
+    credentials = test_docker_interface._get_credentials(
+        "homeassistant/amd64-supervisor"
+    )
+    # docker.io should be preferred
+    assert credentials["username"] == "NewUser"
+    assert "registry" not in credentials