feat: Add Angular, HTML, and SCSS / Sass language servers (#1439)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Pavlo Basanets <Pavlo_Basanets@epam.com>

test/solidlsp/angular/test_angular_diagnostics.py

@@ -0,0 +1,44 @@
+"""
+Diagnostics tests for the Angular language server.
+
+Two paths are exercised:
+  * .ts component — tsserver (via the @angular/language-service plugin) reports
+    the type-mismatch on a class field initializer.
+  * .html template — ngserver reports the unresolved identifier in a template
+    interpolation, but only because the template is attached to a @Component via
+    ``templateUrl``. Bare .html files are not type-checked by ngserver.
+"""
+
+import pytest
+
+from solidlsp import SolidLanguageServer
+from solidlsp.ls_config import Language
+from test.solidlsp.util.diagnostics import assert_file_diagnostics
+
+
+@pytest.mark.angular
+class TestAngularDiagnostics:
+    @pytest.mark.parametrize("language_server", [Language.ANGULAR], indirect=True)
+    def test_component_class_diagnostics(self, language_server: SolidLanguageServer) -> None:
+        """The component's ``count: number = 'not-a-number'`` must be flagged by tsserver."""
+        assert_file_diagnostics(
+            language_server,
+            "src/app/diagnostics_sample.ts",
+            (),
+            min_count=1,
+        )
+
+    @pytest.mark.parametrize("language_server", [Language.ANGULAR], indirect=True)
+    def test_template_diagnostics(self, language_server: SolidLanguageServer) -> None:
+        """The template's ``{{ undefinedSignal() }}`` must be flagged by ngserver.
+
+        Routed through the Angular template compiler, which only checks templates
+        attached to a @Component — see the companion ``diagnostics_sample.ts`` that
+        wires this file via ``templateUrl``.
+        """
+        assert_file_diagnostics(
+            language_server,
+            "src/app/diagnostics_sample.html",
+            (),
+            min_count=1,
+        )