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/workbenchConstants.ts

@@ -236,6 +236,13 @@ export const GRID_MODE_OPTIONS: WorkbenchOption[] = [
   { value: "grid-25", label: "25 宫格" },
 ];
 
+export const GRID_SUPPORTED_MODELS = new Set([
+  "wan2.7-image-pro",
+  "wan2.7-image",
+  "gpt-image-2",
+  "gpt-image-2-vip",
+]);
+
 export const VIDEO_FRAME_OPTIONS: WorkbenchOption[] = [
   { value: "omni", label: "全能参考" },
   { value: "start-end", label: "首尾帧" },