feat(02-06): Account tab in SettingsView + QR code in TotpEnrollment (GAPs 3, 5)

- frontend/package.json: add qrcode@1.5.4 to runtime dependencies
- TotpEnrollment.vue: import QRCode; generate data URL in startSetup(); render img tag
- SettingsAccountTab.vue: new component with all AccountView content (2FA, password, sessions)
- SettingsView.vue: add Account tab rendering SettingsAccountTab; import SettingsAccountTab

frontend/src/components/auth/TotpEnrollment.vue

@@ -28,17 +28,10 @@
             Open your authenticator app and scan this QR code, or enter the key manually.
           </p>
 
-          <!-- QR code — rendered via provisioning URI link (no QR library dependency) -->
+          <!-- QR code — rendered as an inline image via qrcode library -->
           <div class="bg-white border border-gray-200 rounded-xl p-6 flex flex-col items-center gap-4">
-            <p class="text-xs text-gray-500 text-center">Scan with your authenticator app using the link below, or enter the secret key manually:</p>
-            <a
-              :href="qrUri"
-              class="text-sm font-semibold text-indigo-600 hover:text-indigo-700 underline break-all text-center"
-              target="_blank"
-              rel="noopener noreferrer"
-            >
-              Open in authenticator app
-            </a>
+            <p class="text-xs text-gray-500 text-center">Scan this QR code with your authenticator app:</p>
+            <img v-if="qrDataUrl" :src="qrDataUrl" alt="TOTP QR code" class="w-48 h-48 rounded-xl border border-gray-200" />
           </div>
         </div>
 
@@ -115,6 +108,7 @@
 
 <script setup>
 import { ref } from 'vue'
+import QRCode from 'qrcode'
 import * as api from '../../api/client.js'
 import AppSpinner from '../ui/AppSpinner.vue'
 import BackupCodesDisplay from './BackupCodesDisplay.vue'
@@ -123,6 +117,7 @@ const emit = defineEmits(['enrolled'])
 
 const step = ref('setup')
 const qrUri = ref('')
+const qrDataUrl = ref('')
 const secret = ref('')
 const verifyCode = ref('')
 const backupCodes = ref([])
@@ -138,6 +133,7 @@ async function startSetup() {
     const data = await api.totpSetup()
     qrUri.value = data.provisioning_uri
     secret.value = data.secret
+    qrDataUrl.value = await QRCode.toDataURL(qrUri.value, { width: 200, margin: 1 })
     step.value = 'verify'
   } catch (e) {
     error.value = e.message