feat(02-03): TOTP enrollment flow, backup codes, AccountView, ConfirmBlock

- TotpEnrollment.vue: three-step enrollment (setup → verify → backup-codes); emits 'enrolled'
- BackupCodesDisplay.vue: 2-column grid, copy-all clipboard, acknowledgment checkbox
- ConfirmBlock.vue: reusable inline confirmation block with 'confirmed'/'cancelled' emits
- AccountView.vue: TOTP section (enrollment or disable), change-password with breach/wrong-pw error handling, sign-out-all with ConfirmBlock
- npm run build exits 0

frontend/src/components/ui/ConfirmBlock.vue

@@ -0,0 +1,45 @@
+<template>
+  <div class="space-y-3">
+    <p class="text-sm text-gray-700">{{ message }}</p>
+    <div class="flex gap-3 items-center">
+      <button
+        type="button"
+        @click="$emit('cancelled')"
+        class="text-sm text-gray-600 hover:text-gray-800"
+      >
+        {{ cancelLabel }}
+      </button>
+      <button
+        type="button"
+        @click="$emit('confirmed')"
+        class="flex items-center gap-2 px-4 py-2 rounded-lg text-sm font-semibold transition-colors min-h-[44px]"
+        :class="confirmClass || 'bg-red-600 hover:bg-red-700 text-white'"
+      >
+        {{ confirmLabel }}
+      </button>
+    </div>
+  </div>
+</template>
+
+<script setup>
+defineProps({
+  message: {
+    type: String,
+    required: true,
+  },
+  confirmLabel: {
+    type: String,
+    default: 'Confirm',
+  },
+  cancelLabel: {
+    type: String,
+    default: 'Cancel',
+  },
+  confirmClass: {
+    type: String,
+    default: '',
+  },
+})
+
+defineEmits(['confirmed', 'cancelled'])
+</script>