Passwordless-only auth: drop registration and passwords entirely

There is now one way in: POST /api/auth/magic-link with an email address. It
creates the account (unverified) if the address is new -- that's the only
"sign up" -- and emails a sign-in link either way, subject to the existing
60s-per-user resend throttle. Opening the link (POST /api/auth/verify-email,
unchanged) is what actually creates the session, and marks the address
verified the first time. Since a session can now only ever come from an
opened link, "authenticated" implies "verified" -- there's no more
authenticated-but-unverified state, so the resend-verification endpoint and
all the "verify your email" nagging UI are gone too.

Backend
- migrations/008: ALTER TABLE users DROP COLUMN password_hash.
- UserRepository: create() takes only an email; new findOrCreateByEmail()
  (race-safe) backs the magic-link endpoint.
- AuthController: register()/login() removed; requestLoginLink() now
  find-or-creates before sending.
- EmailVerificationController: resend() removed (dead -- you can't be
  authenticated and unverified); requestChange() drops the password check,
  now just { email }.
- EmailVerifier: sendVerification() removed (unused once register() and
  resend() are gone); sendLoginLink() is the one email people get.
- Routes: POST /auth/register, POST /auth/login, POST /email/verification
  all gone.

Frontend
- LoginView: email field + "Send sign-in link" button, nothing else.
  RegisterView and the /register route are gone.
- auth store: register()/login()/resendVerification() removed;
  requestEmailChange() drops the password param.
- ProfileView: password field and the "verify your email" section removed,
  leaving just the change-email form.
- App.vue: the "verify email" header badge is gone; DashboardView's
  unverified-address notice is gone.
- Now-dead .badge/.badge--warn/a.badge CSS removed.

Tests: AuthTest and EmailVerificationTest rewritten for the new flow (52
tests total, down from 58 -- consolidated, not reduced coverage).
ApiTestCase::authHeader() signs in via the real magic-link -> verify flow.

Verified end-to-end against the rebuilt container and the dev server: a brand
new address gets an account + session from one link; /auth/register,
/auth/login and /email/verification all 404; the UI shows no password field
anywhere and no verification nagging. Also fixed the README's "Try it" curl
snippets, which had been silently broken since JSON_PRETTY_PRINT was added
(grep patterns didn't tolerate the space after ':').

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/style.css

@@ -68,10 +68,6 @@ body {
   text-decoration: none;
 }
 
-a.badge {
-  text-decoration: none;
-}
-
 .app__body {
   display: flex;
   align-items: flex-start;
@@ -288,22 +284,6 @@ h1 {
   font-size: 0.85rem;
 }
 
-.badge {
-  padding: 0.1rem 0.45rem;
-  border-radius: 999px;
-  font-size: 0.75rem;
-  white-space: nowrap;
-  border: 1px solid var(--border);
-  background: var(--bg);
-  color: var(--muted);
-}
-
-.badge--warn {
-  border-color: var(--warn-border);
-  background: var(--warn-bg);
-  color: inherit;
-}
-
 /* --- project detail: cards ------------------------------------------ */
 
 .cards {