Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/contexts/toolWorkflow/toolWorkflowState.ts

@@ -0,0 +1,71 @@
+import { PageEditorFunctions } from '@app/types/pageEditor';
+import { type ToolPanelMode, DEFAULT_TOOL_PANEL_MODE } from '@app/constants/toolPanel';
+
+export interface ToolWorkflowState {
+  // UI State
+  sidebarsVisible: boolean;
+  leftPanelView: 'toolPicker' | 'toolContent' | 'hidden';
+  readerMode: boolean;
+  toolPanelMode: ToolPanelMode;
+
+  previewFile: File | null;
+  pageEditorFunctions: PageEditorFunctions | null;
+
+  // Search State
+  searchQuery: string;
+}
+
+// Actions
+export type ToolWorkflowAction =
+  | { type: 'SET_SIDEBARS_VISIBLE'; payload: boolean }
+  | { type: 'SET_LEFT_PANEL_VIEW'; payload: 'toolPicker' | 'toolContent' | 'hidden' }
+  | { type: 'SET_READER_MODE'; payload: boolean }
+  | { type: 'SET_TOOL_PANEL_MODE'; payload: ToolPanelMode }
+  | { type: 'SET_PREVIEW_FILE'; payload: File | null }
+  | { type: 'SET_PAGE_EDITOR_FUNCTIONS'; payload: PageEditorFunctions | null }
+  | { type: 'SET_SEARCH_QUERY'; payload: string }
+  | { type: 'RESET_UI_STATE' };
+
+  
+export const baseState: Omit<ToolWorkflowState, 'toolPanelMode'> = {
+  sidebarsVisible: true,
+  leftPanelView: 'toolPicker',
+  readerMode: false,
+  previewFile: null,
+  pageEditorFunctions: null,
+  searchQuery: '',
+};
+
+export const createInitialState = (): ToolWorkflowState => ({
+  ...baseState,
+  toolPanelMode: DEFAULT_TOOL_PANEL_MODE,
+});
+
+export function toolWorkflowReducer(state: ToolWorkflowState, action: ToolWorkflowAction): ToolWorkflowState {
+  switch (action.type) {
+    case 'SET_SIDEBARS_VISIBLE':
+      return { ...state, sidebarsVisible: action.payload };
+    case 'SET_LEFT_PANEL_VIEW':
+      return { ...state, leftPanelView: action.payload };
+    case 'SET_READER_MODE':
+      return { ...state, readerMode: action.payload };
+    case 'SET_TOOL_PANEL_MODE':
+      return { ...state, toolPanelMode: action.payload };
+    case 'SET_PREVIEW_FILE':
+      return { ...state, previewFile: action.payload };
+    case 'SET_PAGE_EDITOR_FUNCTIONS':
+      return { ...state, pageEditorFunctions: action.payload };
+    case 'SET_SEARCH_QUERY':
+      return { ...state, searchQuery: action.payload };
+    case 'RESET_UI_STATE':
+      return {
+        ...baseState,
+        toolPanelMode: state.toolPanelMode,
+        searchQuery: state.searchQuery,
+      };
+    default:
+      return state;
+  }
+}
+
+