Add passkeys (WebAuthn): register from the profile, log in without email

New library dependency: lbuchs/webauthn (^2.2, MIT, zero transitive deps
beyond PHP+OpenSSL+Mbstring, both already required). 'none' attestation --
this only confirms "the same device that registered", not hardware
provenance, the standard trust model for a public site's own passkey login.

Backend
- migrations/010: `passkeys` (one row per registered credential: owner,
  credential_id, public_key, sign_count, label) and `webauthn_challenges`
  (short-lived, single-use, bridging each ceremony's "options" and "verify"
  calls -- user_id set for a registration, null for a login since who's
  signing in isn't known until the credential comes back).
- Config: WEBAUTHN_RP_ID (defaults to APP_URL's host) and WEBAUTHN_RP_NAME.
- PasskeyRepository, WebAuthnChallengeRepository, PasskeyController:
  GET/POST /api/passkeys, POST /api/passkeys/options, DELETE
  /api/passkeys/{id} (all auth), plus the public POST /api/auth/passkey/
  options and /verify for login. Registration always asks for a
  discoverable, user-verified credential -- what makes login usernameless:
  the browser offers whatever passkeys it has for the site, no email first.
- SessionPayload now also exposes `has_passkey` on every user object
  (PasskeyRepository::countForUser() > 0), reused by both the profile page
  and the dismissible notice.
- PasskeyTest: auth guards, options response shape, challenge single-use/
  expiry/purpose/cross-user rules, malformed-input handling, list/remove
  CRUD (seeded rows) -- everything short of a real signature, which isn't
  practical from PHPUnit. 73 tests pass.

Frontend
- lib/webauthn.ts: base64url <-> ArrayBuffer conversion and the two
  ceremonies (registerPasskey, loginWithPasskey), matching the API's wire
  format exactly.
- ProfileView: a Passkeys section -- list with Remove buttons, an "Add a
  passkey" form (label pre-filled from a UA guess).
- LoginView: a "Log in with a passkey" button above the email form, shown
  only when the browser supports WebAuthn.
- PasskeyNotice.vue: dismissible banner across the top of the page
  (`user.has_passkey === false`); dismissal is a week-long localStorage
  timestamp.

Verified against the rebuilt container using a Chrome DevTools Protocol
*virtual authenticator* (real ECDSA signing, no human interaction) end to
end: notice shown -> register a passkey -> notice gone (same page and after
navigating) -> log out -> "Log in with a passkey" with no email typed ->
correct account, notice still gone -> remove the passkey -> notice back ->
dismiss -> stays hidden for ~7 days across pages. Along the way, caught and
fixed a real bug: AuthenticatorData::getCredentialId() returns a raw binary
string, not a ByteBuffer like most of this library's other binary fields --
bin2hex() it directly rather than calling ->getHex().

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

src/Auth/SessionPayload.php

@@ -5,18 +5,19 @@ declare(strict_types=1);
 namespace App\Auth;
 
 use App\Repository\EmailVerificationRepository;
+use App\Repository\PasskeyRepository;
 
 /**
  * Builds the JSON representation of a user and the session envelope returned
- * when a magic link is opened (sign-up, sign-in, and email-change confirmation
- * all go through the same verify-email endpoint). Shared so every entry point
- * agrees on the shape.
+ * when a magic link (or a passkey) signs someone in. Shared so every entry
+ * point agrees on the shape.
  */
 final class SessionPayload
 {
     public function __construct(
         private readonly JwtService $jwt,
         private readonly EmailVerificationRepository $tokens,
+        private readonly PasskeyRepository $passkeys,
     ) {
     }
 
@@ -49,6 +50,7 @@ final class SessionPayload
             'email_verified' => $verifiedAt !== null,
             'email_verified_at' => $verifiedAt,
             'pending_email' => $this->tokens->pendingEmailFor((int) $user['id']),
+            'has_passkey' => $this->passkeys->countForUser((int) $user['id']) > 0,
             'created_at' => $user['created_at'] ?? null,
         ];
     }