Restructure SAM rough mask workflow for sidebar preview

- Add roughMaskThumbnailScale state with $watch to sync with main scale slider
- Update sidebar thumbnail to use transform:scale() for consistent zoom between views
- Modify openRoughMaskInNewWindow() to create HTML page with matching scale
- Add denoise strength slider (10-100%) visible only when rough mask exists
- Backend already supports denoise_strength parameter in prepare_mask_workflow_with_start()
- Rough mask auto-clears after successful extraction
- Add Playwright tests for UI changes and API parameter acceptance

tools/ora_editor/templates/components/canvas.html

@@ -43,14 +43,6 @@
                 </template>
             </template>
             
-            <!-- SAM mask preview overlay -->
-            <img 
-                x-show="samMaskUrl" 
-                :src="samMaskUrl" 
-                class="absolute inset-0 w-full h-full object-contain pointer-events-none z-15 opacity-50"
-                alt="SAM mask preview"
-            >
-            
             <!-- Polygon points markers (draggable) - shown in add mode -->
             <template x-if="mode === 'add' && polygonPoints.length > 0">
                 <template x-for="(point, idx) in polygonPoints" :key="'point-' + idx">