[cli] Deprecate the dashboard command

The dashboard command is deprecated and will be removed in 2027.1.0.
Standalone pip installs are pointed to the 'esphome-device-builder'
package, and the subcommand is hidden from the main parser help while
remaining functional.

esphome/__main__.py

@@ -1692,6 +1692,11 @@ def command_bundle(args: ArgsProtocol, config: ConfigType) -> int | None:
 
 
 def command_dashboard(args: ArgsProtocol) -> int | None:
+    _LOGGER.warning(
+        "The 'dashboard' command is deprecated and will be removed in ESPHome "
+        "2027.1.0. Install the 'esphome-device-builder' package and run "
+        "'esphome-device-builder' instead."
+    )
     from esphome.dashboard import dashboard
 
     return dashboard.start_dashboard(args)
@@ -2356,9 +2361,9 @@ def parse_args(argv):
         "configuration", help="Your YAML file or configuration directory.", nargs="*"
     )
 
-    parser_dashboard = subparsers.add_parser(
-        "dashboard", help="Create a simple web server for a dashboard."
-    )
+    # Deprecated, will be removed in 2027.1.0. Omitting help= hides it from the
+    # main parser's command listing while keeping the subcommand functional.
+    parser_dashboard = subparsers.add_parser("dashboard")
     parser_dashboard.add_argument(
         "configuration", help="Your YAML configuration file directory."
     )

tests/unit_tests/test_main.py

@@ -32,6 +32,7 @@ from esphome.__main__ import (
     command_clean_all,
     command_config,
     command_config_hash,
+    command_dashboard,
     command_idedata,
     command_rename,
     command_run,
@@ -6283,3 +6284,25 @@ def test_command_idedata_esp_idf_no_build_errors() -> None:
         result = command_idedata(MagicMock(), CORE.config)
 
     assert result == 1
+
+
+def test_command_dashboard_warns_deprecated(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """The dashboard command logs a deprecation warning and still starts."""
+    args = MockArgs()
+
+    with (
+        patch(
+            "esphome.dashboard.dashboard.start_dashboard", return_value=0
+        ) as mock_start,
+        caplog.at_level(logging.WARNING, logger="esphome.__main__"),
+    ):
+        result = command_dashboard(args)
+
+    assert result == 0
+    mock_start.assert_called_once_with(args)
+    assert any(
+        "deprecated" in rec.message and "2027.1.0" in rec.message
+        for rec in caplog.records
+    )