feat: Validate AlwaysSchema and NeverSchema in DefaultValidator

Pins the existing case branches (added in Task 1 to keep the sealed
switch compiling) with seven new unit tests covering pass/reject across
string / integer / object / null inputs for both AlwaysSchema and
NeverSchema.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thced

src/test/java/com/retailsvc/http/validate/DefaultValidatorDispatchTest.java

@@ -5,14 +5,17 @@
 
 import com.retailsvc.http.ValidationException;
 import com.retailsvc.http.spec.schema.AllOfSchema;
+import com.retailsvc.http.spec.schema.AlwaysSchema;
 import com.retailsvc.http.spec.schema.AnyOfSchema;
 import com.retailsvc.http.spec.schema.BooleanSchema;
+import com.retailsvc.http.spec.schema.NeverSchema;
 import com.retailsvc.http.spec.schema.NotSchema;
 import com.retailsvc.http.spec.schema.NullSchema;
 import com.retailsvc.http.spec.schema.OneOfSchema;
 import com.retailsvc.http.spec.schema.StringSchema;
 import com.retailsvc.http.spec.schema.TypeName;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import org.junit.jupiter.api.Test;
 
@@ -172,4 +175,52 @@ void anyOfMatchesNullViaNullSchema() {
     var schema = new AnyOfSchema(List.of(stringSchema(1, null), new NullSchema()));
     v.validate(null, schema, "/v");
   }
+
+  @Test
+  void alwaysSchemaAcceptsString() {
+    v.validate("anything", new AlwaysSchema(), "/v");
+  }
+
+  @Test
+  void alwaysSchemaAcceptsInteger() {
+    v.validate(42, new AlwaysSchema(), "/v");
+  }
+
+  @Test
+  void alwaysSchemaAcceptsObject() {
+    v.validate(Map.of("a", 1), new AlwaysSchema(), "/v");
+  }
+
+  @Test
+  void alwaysSchemaAcceptsNull() {
+    v.validate(null, new AlwaysSchema(), "/v");
+  }
+
+  @Test
+  void neverSchemaRejectsString() {
+    assertThatThrownBy(() -> v.validate("anything", new NeverSchema(), "/v"))
+        .isInstanceOf(ValidationException.class)
+        .satisfies(
+            t -> {
+              var err = ((ValidationException) t).error();
+              assertThat(err.keyword()).isEqualTo("false");
+              assertThat(err.message()).contains("rejects all values");
+            });
+  }
+
+  @Test
+  void neverSchemaRejectsInteger() {
+    assertThatThrownBy(() -> v.validate(42, new NeverSchema(), "/v"))
+        .isInstanceOf(ValidationException.class)
+        .extracting(t -> ((ValidationException) t).error().keyword())
+        .isEqualTo("false");
+  }
+
+  @Test
+  void neverSchemaRejectsNull() {
+    assertThatThrownBy(() -> v.validate(null, new NeverSchema(), "/v"))
+        .isInstanceOf(ValidationException.class)
+        .extracting(t -> ((ValidationException) t).error().keyword())
+        .isEqualTo("false");
+  }
 }