0.5.2: paste images, shared import helper, clipart persistence

- Clipboard paste creates an image layer: a document-level paste
  listener detects image items in the clipboard (Strg+V after a
  screenshot, e.g.) and imports them via the shared helper. Skipped
  when focus is in a real text input / textarea / contenteditable.
- Shared importImageFile() helper in fileLoader.ts replaces the
  duplicated image-import logic in AssetSidebar and CanvasStage's
  clipart-drop path. Optional position argument for drop-at-point.
- Clipart folder persistence hardened for reloads:
  - initialize() is now safely re-runnable (no-ops only once a handle
    is actually loaded, tolerates refresh failures so the folder name
    survives even if permission isn't auto-granted)
  - App.vue's onMounted kicks off initialize() so it runs regardless
    of whether the drawer component has mounted
  - DocumentSettings re-invokes initialize() each time the modal
    opens — covers app-start races and gives the user gesture needed
    for FS Access permission prompts
  - Opening the drawer refreshes thumbnails when handle is set but
    items are empty, so the user-gesture context restores permission

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/stores/clipart.ts

@@ -51,14 +51,27 @@ export const useClipartStore = defineStore('clipart', {
   }),
   actions: {
     async initialize() {
-      if (this.initialized) return
-      this.initialized = true
-      if (!this.supported) return
+      if (!this.supported) {
+        this.initialized = true
+        return
+      }
+      // Safe to call multiple times; a second call will no-op once a handle
+      // has been loaded. If the previous attempt failed silently (e.g. IDB
+      // race on app start), a later call from Settings/drawer can retry.
+      if (this.handle) {
+        this.initialized = true
+        return
+      }
       const handle = await loadStoredClipartFolder()
+      this.initialized = true
       if (!handle) return
       this.handle = handle
       this.folderName = handle.name
-      await this.refresh()
+      try {
+        await this.refresh()
+      } catch {
+        /* permission may require a user gesture; items will populate on next open */
+      }
     },
     async pickFolder() {
       this.error = null
@@ -105,6 +118,10 @@ export const useClipartStore = defineStore('clipart', {
     setOpen(v: boolean) {
       this.open = v
       writeDrawerOpen(v)
+      if (v && this.handle && this.items.length === 0 && !this.loading) {
+        // User gesture opens the drawer — good moment to (re-)request access
+        void this.refresh()
+      }
     },
     toggle() {
       this.setOpen(!this.open)