Replace inconsistent error display patterns across views:
- addWallet.js: replace showFlash() with showError('add-wallet-error', ...)
- importKey.js: replace showFlash() with showError('import-key-error', ...)
- addressDetail.js: replace direct DOM manipulation of export-privkey-flash
with showError/hideError('export-privkey-error', ...)
- deleteWallet.js: replace direct DOM manipulation of delete-wallet-flash
with showError/hideError('delete-wallet-error', ...)
- index.html: add dedicated error divs with min-h-[1.25rem] for add-wallet,
import-key views; rename flash divs to error divs for export-privkey and
delete-wallet views with consistent styling
All password/validation errors now use the showError()/hideError() helper
pattern with min-h-[1.25rem] error divs to prevent layout shift.
Status/success messages (scanning, wallet deleted) remain as showFlash().
Closes#87
