fix: add missing aria-live to form error messages (#3874)

[Nixxx19]

Fixes #3874

Changes:

• Added aria-live="assertive" to the submit-level error in LoginForm.tsx so screen readers announce "invalid credentials" on failed login
• Audited entire codebase and added missing aria-live to all other form-error spans for consistency:
  • ResetPasswordForm.tsx — 1 field error (aria-live="polite")
  • AccountForm.tsx — 4 field errors (aria-live="polite")
  • NewPasswordForm.tsx — 2 field errors (aria-live="polite")
  • CollectionCreate.jsx — 1 submit error (aria-live="assertive") + 1 validation error (aria-live="polite")
  • NewFileForm.jsx — 1 field error (aria-live="polite")
  • NewFolderForm.jsx — 1 field error (aria-live="polite")

Used aria-live="polite" for per-field validation errors (matching existing pattern in LoginForm.tsx and SignupForm.tsx) and aria-live="assertive" for submit-level errors. This resolves the WCAG 2.2 SC 4.1.3 (Status Messages) violation.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines

[Nixxx19]

hi @raclim, sorry to bother you again!
i also wanted to check in on this accessibility fix for form error messages. it ensures screen readers properly announce errors, which helps with WCAG compliance. whenever you have a moment to review, i'd really appreciate it!