feat(html): add context identity setter

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

context.go

@@ -102,6 +102,18 @@ func (ctx *Context) SetService(svc Translator) *Context {
 	return ctx
 }
 
+// SetIdentity updates the context identity and returns the same context.
+// Example: ctx.SetIdentity("user-123").
+func (ctx *Context) SetIdentity(identity string) *Context {
+	if ctx == nil {
+		return nil
+	}
+
+	ensureContextDefaults(ctx)
+	ctx.Identity = identity
+	return ctx
+}
+
 // SetLocale updates the context locale and reapplies it to the active
 // translator.
 // Example: ctx.SetLocale("en-US").

context_test.go

@@ -96,9 +96,26 @@ func TestContext_SetService_ReappliesCurrentLocale(t *testing.T) {
 	}
 }
 
+func TestContext_SetIdentity_UpdatesIdentity(t *testing.T) {
+	ctx := NewContext()
+
+	if got := ctx.SetIdentity("user-123"); got != ctx {
+		t.Fatalf("SetIdentity should return the same context")
+	}
+	if ctx.Identity != "user-123" {
+		t.Fatalf("SetIdentity should update context identity, got %q", ctx.Identity)
+	}
+	if ctx.Data == nil {
+		t.Fatal("SetIdentity should preserve initialised Data map")
+	}
+}
+
 func TestContext_Setters_NilReceiver(t *testing.T) {
 	var ctx *Context
 
+	if got := ctx.SetIdentity("user-123"); got != nil {
+		t.Fatalf("nil Context.SetIdentity should return nil, got %v", got)
+	}
 	if got := ctx.SetLocale("en-GB"); got != nil {
 		t.Fatalf("nil Context.SetLocale should return nil, got %v", got)
 	}