refactor: Enhance Assembly Editor with Language Definition and Toolset Integration

- Introduced a new language definition for the 65816 assembly language, improving syntax highlighting and code editing capabilities.
- Updated the AssemblyEditor to utilize the new language definition and integrated a toolset for file management actions, enhancing user experience.
- Refactored the file handling logic to support dynamic file opening and saving, ensuring better resource management within the editor.
- Removed deprecated tab view code, transitioning to a more modular card-based layout for active files, improving UI responsiveness and organization.

src/app/editor/sprite/sprite_editor.cc

@@ -1,6 +1,7 @@
 #include "sprite_editor.h"
 
 #include "app/gfx/performance_profiler.h"
+#include "gui/ui_helpers.h"
 #include "util/file_util.h"
 #include "app/editor/sprite/zsprite.h"
 #include "app/gfx/arena.h"
@@ -36,21 +37,40 @@ absl::Status SpriteEditor::Update() {
     sheets_loaded_ = true;
   }
 
-  if (ImGui::BeginTabBar("##SpriteEditorTabs")) {
-    if (ImGui::BeginTabItem("Vanilla")) {
-      DrawVanillaSpriteEditor();
-      ImGui::EndTabItem();
-    }
-    if (ImGui::BeginTabItem("Custom")) {
-      DrawCustomSprites();
-      ImGui::EndTabItem();
-    }
-    ImGui::EndTabBar();
+  DrawToolset();
+  gui::VerticalSpacing(2.0f);
+
+  static gui::EditorCard vanilla_card("Vanilla Sprites", ICON_MD_PEST_CONTROL_RODENT);
+  static gui::EditorCard custom_card("Custom Sprites", ICON_MD_ADD_MODERATOR);
+
+  if (show_vanilla_editor_ && vanilla_card.Begin(&show_vanilla_editor_)) {
+    DrawVanillaSpriteEditor();
+    vanilla_card.End();
+  }
+
+  if (show_custom_editor_ && custom_card.Begin(&show_custom_editor_)) {
+    DrawCustomSprites();
+    custom_card.End();
   }
 
   return status_.ok() ? absl::OkStatus() : status_;
 }
 
+void SpriteEditor::DrawToolset() {
+  static gui::Toolset toolbar;
+  toolbar.Begin();
+
+  if (toolbar.AddAction(ICON_MD_PEST_CONTROL_RODENT, "Vanilla Sprites")) {
+    show_vanilla_editor_ = !show_vanilla_editor_;
+  }
+  if (toolbar.AddAction(ICON_MD_ADD_MODERATOR, "Custom Sprites")) {
+    show_custom_editor_ = !show_custom_editor_;
+  }
+
+  toolbar.End();
+}
+
+
 void SpriteEditor::DrawVanillaSpriteEditor() {
   if (ImGui::BeginTable("##SpriteCanvasTable", 3, ImGuiTableFlags_Resizable,
                         ImVec2(0, 0))) {