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>

web/src/views/ProfileView.vue

@@ -1,7 +1,9 @@
 <script setup lang="ts">
-import { onBeforeUnmount, ref } from 'vue'
-import { ApiError } from '../lib/api'
+import { onBeforeUnmount, onMounted, ref } from 'vue'
+import { ApiError, apiRequest } from '../lib/api'
+import { passkeysSupported, registerPasskey } from '../lib/webauthn'
 import { useAuthStore } from '../stores/auth'
+import type { Passkey } from '../types'
 
 const auth = useAuthStore()
 
@@ -41,6 +43,80 @@ async function onChangeEmail() {
     changing.value = false
   }
 }
+
+// --- passkeys ------------------------------------------------------------
+const supported = passkeysSupported()
+const passkeys = ref<Passkey[]>([])
+const loadingPasskeys = ref(true)
+const passkeysError = ref('')
+
+const newLabel = ref(guessDeviceLabel())
+const adding = ref(false)
+const addError = ref('')
+const removingId = ref<number | null>(null)
+
+function guessDeviceLabel(): string {
+  const ua = typeof navigator === 'undefined' ? '' : navigator.userAgent
+  if (/iPhone/.test(ua)) return 'iPhone'
+  if (/iPad/.test(ua)) return 'iPad'
+  if (/Android/.test(ua)) return 'Android device'
+  if (/Macintosh/.test(ua)) return 'Mac'
+  if (/Windows/.test(ua)) return 'Windows PC'
+  if (/Linux/.test(ua)) return 'Linux PC'
+  return 'This device'
+}
+
+onMounted(loadPasskeys)
+
+async function loadPasskeys() {
+  if (!supported) {
+    loadingPasskeys.value = false
+    return
+  }
+  loadingPasskeys.value = true
+  passkeysError.value = ''
+  try {
+    const { passkeys: fetched } = await apiRequest<{ passkeys: Passkey[] }>('/passkeys', { auth: true })
+    passkeys.value = fetched
+  } catch (e) {
+    passkeysError.value = e instanceof ApiError ? e.message : 'Could not load your passkeys.'
+  } finally {
+    loadingPasskeys.value = false
+  }
+}
+
+async function onAddPasskey() {
+  adding.value = true
+  addError.value = ''
+  try {
+    const passkey = await registerPasskey(newLabel.value.trim() || guessDeviceLabel())
+    passkeys.value.push(passkey)
+    newLabel.value = guessDeviceLabel()
+    await auth.fetchMe() // clears the "add a passkey" notice once there's one
+  } catch (e) {
+    if (e instanceof DOMException && e.name === 'NotAllowedError') {
+      addError.value = 'Cancelled.'
+    } else {
+      addError.value = e instanceof ApiError ? e.message : 'Could not add that passkey.'
+    }
+  } finally {
+    adding.value = false
+  }
+}
+
+async function onRemovePasskey(passkey: Passkey) {
+  removingId.value = passkey.id
+  passkeysError.value = ''
+  try {
+    await apiRequest(`/passkeys/${passkey.id}`, { method: 'DELETE', auth: true })
+    passkeys.value = passkeys.value.filter((p) => p.id !== passkey.id)
+    await auth.fetchMe() // the notice comes back if that was the last one
+  } catch (e) {
+    passkeysError.value = e instanceof ApiError ? e.message : 'Could not remove that passkey.'
+  } finally {
+    removingId.value = null
+  }
+}
 </script>
 
 <template>
@@ -81,5 +157,54 @@ async function onChangeEmail() {
         </button>
       </form>
     </section>
+
+    <section>
+      <h2>Passkeys</h2>
+
+      <template v-if="!supported">
+        <p class="muted">Passkeys aren't supported in this browser.</p>
+      </template>
+
+      <template v-else>
+        <p class="muted">
+          Sign in with your device's fingerprint, face, or PIN instead of an
+          email link. You can add more than one, e.g. for a phone and a laptop.
+        </p>
+
+        <p v-if="passkeysError" class="form-error">{{ passkeysError }}</p>
+        <p v-else-if="loadingPasskeys" class="muted">Loading…</p>
+        <p v-else-if="passkeys.length === 0" class="muted">No passkeys yet.</p>
+
+        <ul v-else class="passkeys">
+          <li v-for="passkey in passkeys" :key="passkey.id" class="passkeys__item">
+            <div class="passkeys__info">
+              <span class="passkeys__label">{{ passkey.label }}</span>
+              <span class="passkeys__meta muted">
+                {{ passkey.last_used_at ? `Last used ${new Date(passkey.last_used_at).toLocaleDateString()}` : 'Never used' }}
+              </span>
+            </div>
+            <button
+              type="button"
+              class="passkeys__remove"
+              :disabled="removingId === passkey.id"
+              @click="onRemovePasskey(passkey)"
+            >
+              {{ removingId === passkey.id ? 'Removing…' : 'Remove' }}
+            </button>
+          </li>
+        </ul>
+
+        <form class="form form--new-card" @submit.prevent="onAddPasskey">
+          <label>
+            <span>Label</span>
+            <input v-model="newLabel" type="text" maxlength="100" />
+          </label>
+          <p v-if="addError" class="form-error">{{ addError }}</p>
+          <button type="submit" :disabled="adding">
+            {{ adding ? 'Waiting for your passkey…' : 'Add a passkey' }}
+          </button>
+        </form>
+      </template>
+    </section>
   </section>
 </template>