refactor: consolidate workspace spinner and shiftDown state

- Replace manual keydown/keyup listeners with useMagicKeys for shiftDown

- Move app.extensionManager assignment to App.vue

- Remove init() wrapper function in GraphView.vue

Amp-Thread-ID: https://ampcode.com/threads/T-019bf90e-1cd0-71de-b23f-ea6cb0f99a87
Co-authored-by: Amp <amp@ampcode.com>

src/stores/workspaceStore.ts

@@ -1,3 +1,4 @@
+import { useMagicKeys } from '@vueuse/core'
 import { defineStore } from 'pinia'
 import { computed, ref } from 'vue'
 
@@ -18,7 +19,7 @@ import { useSidebarTabStore } from './workspace/sidebarTabStore'
 
 export const useWorkspaceStore = defineStore('workspace', () => {
   const spinner = ref(false)
-  const shiftDown = ref(false)
+  const { shift: shiftDown } = useMagicKeys()
   /**
    * Whether the workspace is in focus mode.
    * When in focus mode, only the graph editor is visible.