feat: invite-acceptance page — set password to activate an invited volunteer account

[arturasmckwcz]

Why

Part of the epic: need4deed-org/be#922. Backend (need4deed-org/be#920) emails invited
volunteers a link with a token; this is the page that link lands on, where
they set a password and activate their account.

Scope

• Depends on the SDK contract from feat: accept-invite request/response contract for volunteer account linking sdk#212 being published — pin
  need4deed-sdk to that version before starting.
• New route, e.g. src/app/[lang]/invite/volunteer/[token]/page.tsx (or
  reuse verify-email/[token] with a role marker — decide during TODO
  review, once the backend endpoint shape from feat: invite flow — mint invite tokens for volunteers, accept-invite endpoint be#920 is
  final).
• UI: reuse ResetPasswordForm's password + confirm-password fields and
  validation (resetPasswordSchema.ts) as a base rather than rebuilding it.
• On submit: POST to the new accept-invite endpoint (decide during TODO
  review, once feat: invite flow — mint invite tokens for volunteers, accept-invite endpoint be#920 lands) with the
  token + password via useMutationQuery (repo convention — not a raw
  axios.post).
• On success: call setAuthHint() and redirect to /dashboard, matching
  the existing ProfileCompletion flow for agent registration.
• Add the new route segment to the no-redirect-on-401 allowlist in
  src/config/axios.ts (currently login, forms, register) so a stale
  or anonymous session doesn't hijack the flow mid-invite.
• Add copy under a new translations.json namespace (mirror the
  agentRegistration namespace's shape) in both
  public/locales/en/translations.json and
  public/locales/de/translations.json.

Acceptance criteria

• Page renders for a valid, unexpired token and lets the user set a
  password
• Expired / invalid / already-used tokens show a clear error state (no
  silent failure)
• On success, the user lands authenticated on /dashboard
• New route added to axios's no-redirect allowlist
• Copy present in both en and de locale files