L49: Remove newline from missing-binary error message in download.ts; inline
error spans render it as literal newline, now one sentence with period.
L53: backup.ts exportBackup/importBackup/showMessageBox no longer use win!
non-null assertions -- each uses a guarded ternary (same pattern index.ts
already used for chooseFolder).
L59: Extract PAGE_BACKGROUND to src/shared/theme.ts; main/index.ts and
renderer/src/theme.ts both import from it -- no more "keep in sync" comment.
typecheck + 242 tests + eslint + prettier green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
