feat: add canvas tool panels (multi-grid, upscale, inpaint) and conditional grid mode

Add modal-based tool panels for multi-grid, super-resolution, and inpaint in canvas image-to-image workflow. Grid mode selector only appears for models that support multi-image generation (wan2.7-image, gpt-image-2). Also fixes merge conflict markers in CSS and adds missing toast import.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/features/workbench/WorkbenchPage.tsx

@@ -109,6 +109,7 @@ import {
   VIDEO_MODEL_OPTIONS,
   RATIO_OPTIONS,
   GRID_MODE_OPTIONS,
+  GRID_SUPPORTED_MODELS,
   VIDEO_FRAME_OPTIONS,
   VIDEO_DURATION_OPTIONS,
   MESSAGE_STORAGE_KEY,
@@ -2729,7 +2730,7 @@ function WorkbenchPage({
               isOpen={toolbarMenuId === "image-model"}
               onToggle={() => toggleToolbarMenu("image-model")}
               onClose={closeToolbarMenus}
-              onChange={setImageModel}
+              onChange={(v) => { setImageModel(v); if (!GRID_SUPPORTED_MODELS.has(v)) setImageGridMode("single"); }}
               direction={dropdownDirection}
             />
             <CompoundSelectChip
@@ -2741,6 +2742,7 @@ function WorkbenchPage({
               onToggle={() => toggleToolbarMenu("image-settings")}
               direction={dropdownDirection}
             />
+            {GRID_SUPPORTED_MODELS.has(imageModel) && (
             <SelectChip
               chipId="image-grid-mode"
               value={imageGridMode}
@@ -2752,6 +2754,7 @@ function WorkbenchPage({
               onChange={setImageGridMode}
               direction={dropdownDirection}
             />
+            )}
           </>
         )}
         {activeMode === "video" && (