Add context menu icons, expand empty-area menu, add test_context_menu

- Right-click on empty area: Add Hex64, Add Struct, Append 128 bytes,
  Undo/Redo, Copy All as Text (with icons for each)
- Right-click on node: icons for Edit Value, Rename, Change Type,
  Add Field, Add Child, Expand/Collapse, Duplicate, Delete,
  Copy Address, Copy Offset, Copy All as Text
- Multi-select menu: icons for batch delete and batch change type
- Add test_context_menu.cpp (20 tests): insert adds exactly one node,
  auto-offset placement, duplicate adds exactly one copy, duplicate
  preserves original, duplicate undo, struct duplicate no-op, root
  insert, append 128 bytes (16 nodes), append undo (macro), insert
  child, remove+undo, multiple duplicates, parent correctness, struct
  with children, batch remove, invalid parent, invalid index guards
- Add vsicons to qrc: trash, clippy, link, diff-added, expand-all,
  collapse-all, rename, whole-word, list-selection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CMakeLists.txt

@@ -143,4 +143,13 @@ if(BUILD_TESTING)
     target_include_directories(test_generator PRIVATE src)
     target_link_libraries(test_generator PRIVATE Qt6::Core Qt6::Test)
     add_test(NAME test_generator COMMAND test_generator)
+
+    add_executable(test_context_menu tests/test_context_menu.cpp
+        src/editor.cpp src/compose.cpp src/format.cpp src/controller.cpp
+        src/processpicker.cpp src/processpicker.ui)
+    target_include_directories(test_context_menu PRIVATE src)
+    target_link_libraries(test_context_menu PRIVATE
+        Qt6::Widgets Qt6::PrintSupport Qt6::Test
+        QScintilla::QScintilla dbghelp psapi)
+    add_test(NAME test_context_menu COMMAND test_context_menu)
 endif()