feat(html): add cloneable identity helper

Co-Authored-By: Virgil <virgil@lethean.io>

context.go

@@ -155,6 +155,17 @@ func (ctx *Context) WithData(key string, value any) *Context {
 	return clone
 }
 
+// WithIdentity returns a cloned context with a different identity value.
+// Example: next := ctx.WithIdentity("user-123").
+func (ctx *Context) WithIdentity(identity string) *Context {
+	clone := ctx.Clone()
+	if clone == nil {
+		return nil
+	}
+	clone.SetIdentity(identity)
+	return clone
+}
+
 // SetLocale updates the context locale and reapplies it to the active
 // translator.
 // Example: ctx.SetLocale("en-US").

context_test.go

@@ -181,6 +181,27 @@ func TestContext_WithDataReturnsClonedContext(t *testing.T) {
 	}
 }
 
+func TestContext_WithIdentityReturnsClonedContext(t *testing.T) {
+	ctx := NewContext()
+	ctx.SetIdentity("user-001")
+	ctx.SetData("theme", "dark")
+
+	next := ctx.WithIdentity("user-123")
+
+	if next == ctx {
+		t.Fatal("WithIdentity should return a cloned context")
+	}
+	if got := ctx.Identity; got != "user-001" {
+		t.Fatalf("WithIdentity should not mutate the original context, got %q", got)
+	}
+	if got := next.Identity; got != "user-123" {
+		t.Fatalf("WithIdentity should set the requested identity on the clone, got %q", got)
+	}
+	if got := next.Data["theme"]; got != "dark" {
+		t.Fatalf("WithIdentity should preserve existing data on the clone, got %v", got)
+	}
+}
+
 func TestContext_Setters_NilReceiver(t *testing.T) {
 	var ctx *Context