[backport core/1.35] Fix: Minimap rendering (#7725)

## Summary
- Backport of #7639 to core/1.35
- Cherry-picked merge commit 6d57b4def5
- Resolved conflicts in test snapshot PNGs (accepted PR version for all
changed snapshots)

## Original PR
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7639

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7725-backport-core-1-35-Fix-Minimap-rendering-2d16d73d36508164a229e35d18ce515e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

tests-ui/tests/renderer/extensions/minimap/composables/useMinimapInteraction.test.ts

@@ -280,7 +280,7 @@ describe('useMinimapInteraction', () => {
   })
 
   it('should handle null container gracefully', () => {
-    const containerRef = ref<HTMLDivElement | undefined>(undefined)
+    const containerRef = ref<HTMLDivElement | null>(null)
     const boundsRef = ref({ minX: 0, minY: 0, width: 500, height: 400 })
     const scaleRef = ref(0.5)
     const canvasRef = ref(mockCanvas as any)

tests-ui/tests/renderer/extensions/minimap/composables/useMinimapRenderer.test.ts

@@ -1,5 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
-import { ref } from 'vue'
+import { ref, shallowRef } from 'vue'
 
 import type { LGraph } from '@/lib/litegraph/src/litegraph'
 import { useMinimapRenderer } from '@/renderer/extensions/minimap/composables/useMinimapRenderer'
@@ -32,7 +32,7 @@ describe('useMinimapRenderer', () => {
   })
 
   it('should initialize with full redraw needed', () => {
-    const canvasRef = ref(mockCanvas)
+    const canvasRef = shallowRef<HTMLCanvasElement | null>(mockCanvas)
     const graphRef = ref(mockGraph as any)
     const boundsRef = ref({ minX: 0, minY: 0, width: 100, height: 100 })
     const scaleRef = ref(1)
@@ -230,7 +230,7 @@ describe('useMinimapRenderer', () => {
   })
 
   it('should handle null canvas gracefully', () => {
-    const canvasRef = ref<HTMLCanvasElement | undefined>(undefined)
+    const canvasRef = shallowRef<HTMLCanvasElement | null>(null)
     const graphRef = ref(mockGraph as any)
     const boundsRef = ref({ minX: 0, minY: 0, width: 100, height: 100 })
     const scaleRef = ref(1)