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/styles/pages/script-tokens-v5.css

@@ -3577,8 +3577,6 @@
     font-size: 13px;
   }
 }
-<<<<<<< HEAD
-=======
 
 /* Script review left panel overflow guard: keep actions available while history remains scrollable. */
 .script-eval-v5-left {
@@ -4087,4 +4085,3 @@
 .script-eval-v5.is-ready .script-eval-v5-status-dot {
   box-shadow: none;
 }
->>>>>>> c1c4086383ddd7c1c8c152c2d5a97a4f432fa260