fix(auth): polish login/register/reset pages for consistency and accessibility

- LoginPage: add client-side email/password validation (inline error +
  helperText, matching the 2FA components' established pattern), and a
  proper register-mode toggle with a "Confirm password" field. The
  brief asked for confirm-password on registration but the page only
  had one shared password field; a toggle (mirroring the existing
  Tabs-for-mode pattern already used for Google/Microsoft) keeps this
  from cluttering the login form for returning users.
- Fix a real bug in ResetPasswordPage: it didn't use the app's
  getApiErrorMessage helper, so a non-string error response body would
  render as "[object Object]" in the toast. Also add a confirm-password
  field and matching client-side validation for parity with register.
- ForgotPasswordPage: add proper email format validation instead of
  only checking for non-empty.
- Add matching i18n keys (en/no) for every new validation message.

Verified live end-to-end against a running backend: register-mode
toggle, confirm-password mismatch blocking submission client-side,
and a full registration completing and landing on the dashboard.

job-tracker-ui/src/i18n/translations.ts

@@ -768,6 +768,12 @@ export const translations = {
     passwordResetRequestSent: "If that account exists, a reset link has been sent.",
     passwordResetRequestFailed: "Could not send the reset link.",
     loginFailed: "Login failed.",
+    emailRequired: "Enter your email address.",
+    invalidEmail: "Enter a valid email address.",
+    passwordRequired: "Enter your password.",
+    passwordTooShort: "Password must be at least 8 characters, with a number and a lowercase letter.",
+    confirmPassword: "Confirm password",
+    passwordsDoNotMatch: "Passwords do not match.",
     resetPasswordTitle: "Reset password",
     resetPasswordBody: "Set a new password for your account.",
     missingResetLinkInfo: "Missing email/token in link.",
@@ -1816,6 +1822,12 @@ export const translations = {
     passwordResetRequestSent: "Hvis kontoen finnes, er en nullstillingslenke sendt.",
     passwordResetRequestFailed: "Kunne ikke sende nullstillingslenken.",
     loginFailed: "Innlogging mislyktes.",
+    emailRequired: "Skriv inn e-postadressen din.",
+    invalidEmail: "Skriv inn en gyldig e-postadresse.",
+    passwordRequired: "Skriv inn passordet ditt.",
+    passwordTooShort: "Passordet må være minst 8 tegn, med et tall og en liten bokstav.",
+    confirmPassword: "Bekreft passord",
+    passwordsDoNotMatch: "Passordene stemmer ikke overens.",
     resetPasswordTitle: "Tilbakestill passord",
     resetPasswordBody: "Sett et nytt passord for kontoen din.",
     missingResetLinkInfo: "Mangler e-post/token i lenken.",