v2.2.0

fix: filter 0-byte frames in save/restore + show validImageCount in dialog

On-demand video mode stores unloaded frames as new File([], name) empty
placeholders. AutoSaveService serialized these as 0-byte ArrayBuffers into
IndexedDB, and FileUtil.loadImage fails silently on them, leaving all
thumbnails spinning forever after restore.

• AutoSaveService: drop entries with byteLength=0 before writing to IDB
• IndexedDBManager.getProjectMeta(): add validImageCount (non-zero entries)
  and count annotated images from valid entries only
• hasStoredProject(): use validImageCount instead of imageCount
• ProjectRestoreService.checkForStoredData(): expose validImageCount
• ProjectRestoreService.restoreProject(): skip 0-byte frames before dispatch
• App.tsx: show "可恢复帧 X/Y" row in restore dialog when counts differ,
  highlight in orange when validImageCount=0
• App.scss: add .warn color for zero-recoverable warning

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com