fix(print): prevent white page when persisted state JSON is invalid

[akira69]

Summary

Prevents blank-page failures when persisted frontend state is malformed. This stays a frontend-only robustness fix scoped to saved-state recovery and spool print base_url handling.

What Changed

• useSavedState(...) now validates parsed values against the expected shape, removes malformed savedStates-* entries, and avoids writing "undefined" back to localStorage when state is unset.
• useInitialTableState(...) now validates saved sorters, filters, pagination, and show-columns state, removes malformed localStorage/hash entries, and normalizes legacy pagination from { current } to { currentPage }.
• client/src/pages/printing/spoolQrCodePrintingDialog.tsx now accepts legacy raw-string base_url values, ignores unusable non-string values, and falls back to window.location.origin when no usable value exists.

Testing Performed

• cd client && ./node_modules/.bin/eslint src/utils/saveload.ts src/pages/printing/spoolQrCodePrintingDialog.tsx
• cd client && ./node_modules/.bin/prettier --check src/utils/saveload.ts src/pages/printing/spoolQrCodePrintingDialog.tsx
• cd client && VITE_APIURL=/api/v1 npm run build
• PATH=.venv/bin:$PATH SPOOLMAN_DIR_DATA=/tmp/spoolman_pr_871_data uv run uvicorn spoolman.main:app --host 0.0.0.0 --port 9871
• Real Playwright validation on http://localhost:9871 covering:
  • malformed savedStates-* on /spool/print?spools=1&return=%2Fspool%2Fprint
  • malformed savedStates-spoolList-showArchived plus malformed spoolList-v2-* localStorage on /spool
  • malformed #sorters, #filters, and legacy #pagination hash state on /spool
  • raw-string base_url
  • empty/default base_url fallback to window.location.origin

Test Checklist

• /spool/print?spools=1&return=%2Fspool%2Fprint renders with malformed savedStates-*
• /spool renders with malformed saved table localStorage
• malformed hash state is cleaned up and legacy pagination is normalized
• raw-string base_url is accepted on spool print
• empty/default base_url falls back to window.location.origin