i18n: extract Authorization screens into a new auth namespace (Part of #145)

[everysingletear]

Part of #145. Replaces #168, which was extracted against the pre-revamp screens and could not be rebased — the zone had been reshaped enough that the old hunks had nothing left to apply to. This is a fresh extraction against current develop.

Every user-facing string under src/views/Authorization/ moves into a new auth namespace. English only — no translations here, so it is language-agnostic and reviewable as a pure refactor.

What moves

Screen	Covered
LoginView	primary/sub-account tabs, credential form, social and Authentik buttons, welcome-back state, every auth error toast
Signup	account creation form and each field-validation message
ForgotPasswordView	reset request flow and its toasts
UpdatePasswordView	new-password entry, including mismatch and length errors
Authenticating	the OAuth landing screen and its MFA branches
MFAVerificationModal	code entry, backup codes, error states
AuthFields / LoginSettings	shared field labels and the server settings panel

auth is registered in src/i18n/config.js; public/locales/en/auth.json holds the 103 keys. Your Crowdin config picks up /public/locales/en/*.json by glob, so the namespace flows into the pipeline with no change to crowdin.yml.

On "no behaviour change"

Every t() value is the string that rendered before, character for character — checked mechanically against this branch's base rather than by eye, across all 130 call sites.

The e2e suite is a second, independent check: it selects auth controls by visible text (getByRole('button', { name: 'Create account' }), getByText('Username must be at least 4 characters')), so a green auth.spec.js means nothing rendered differently.

The one place the diff isn't purely mechanical

AuthPasswordField had label = 'Password' as a prop default, and neither LoginView nor Signup passed a label. A prop default is evaluated at module scope, where t isn't available, so the label moves to the call sites and both now pass it explicitly. Same rendered output; flagging it because it is the only structural change in the diff.

AuthDivider had children = 'or' for the same reason — it now falls back to t('or') when no children are given.

Scope notes

MFAVerificationModal is included this time. I left it out of #168 because it looked entangled with the MFA flow; on a second read it isn't — the diff there is string replacement only. Authenticating.jsx is included for a similar reason: it sits in the same zone, and leaving it hardcoded would only have meant a follow-up round.

Rebased on current develop; build is green.

[meauxt]

@everysingletear Thank you <3