Implement code word based remote authentication (#1)

Add comprehensive remote authentication system allowing users to log in from one device by authenticating from another trusted device. Features include:

- Proof of Work (PoW) protection using PBKDF2-SHA512 to prevent abuse
- Simple pairing codes (3 words) protected by dynamic PoW difficulty
- Autocomplete pairing code input with error checking
- Real-time WebSocket communication between devices

Unlike device addition links and reset links with QR codes that only allow adding an authentication method, and that work offline over the duration of several days, this mechanism is strictly online, with 5 minute time limit.

frontend/src/components/UserBasicInfo.vue

@@ -1,5 +1,5 @@
 <template>
-  <div v-if="userLoaded" class="user-info">
+  <div v-if="userLoaded" class="user-info" :class="{ 'has-extra': $slots.default }">
     <h3 class="user-name-heading">
       <span class="icon">👤</span>
       <span class="user-name-row">
@@ -11,12 +11,15 @@
       <div class="org-line" v-if="orgDisplayName">{{ orgDisplayName }}</div>
       <div class="role-line" v-if="roleName">{{ roleName }}</div>
     </div>
-    <span><strong>Visits:</strong></span>
-    <span>{{ visits || 0 }}</span>
-    <span><strong>Registered:</strong></span>
-    <span>{{ formatDate(createdAt) }}</span>
-    <span><strong>Last seen:</strong></span>
-    <span>{{ formatDate(lastSeen) }}</span>
+    <span class="info-label"><strong>Visits:</strong></span>
+    <span class="info-value">{{ visits || 0 }}</span>
+    <span class="info-label"><strong>Registered:</strong></span>
+    <span class="info-value">{{ formatDate(createdAt) }}</span>
+    <span class="info-label"><strong>Last seen:</strong></span>
+    <span class="info-value">{{ formatDate(lastSeen) }}</span>
+    <div v-if="$slots.default" class="user-info-extra">
+      <slot></slot>
+    </div>
   </div>
 </template>
 
@@ -44,13 +47,50 @@ const userLoaded = computed(() => !!props.name)
 </script>
 
 <style scoped>
-.user-info { display: grid; grid-template-columns: auto 1fr; gap: 10px; }
-.user-info h3 { grid-column: span 2; }
-.org-role-sub { grid-column: span 2; display:flex; flex-direction:column; margin: -0.15rem 0 0.25rem; }
+.user-info.has-extra {
+  grid-template-columns: auto 1fr;
+  grid-template-areas:
+    "heading heading"
+    "org org"
+    "label1 value1"
+    "label2 value2"
+    "label3 value3"
+    "extra extra";
+}
+
+.user-info:not(.has-extra) {
+  grid-template-columns: auto 1fr;
+  grid-template-areas:
+    "heading heading"
+    "org org"
+    "label1 value1"
+    "label2 value2"
+    "label3 value3";
+}
+
+@media (min-width: 769px) {
+  .user-info.has-extra {
+    grid-template-columns: auto 1fr 2fr;
+    grid-template-areas:
+      "heading heading extra"
+      "org org extra"
+      "label1 value1 extra"
+      "label2 value2 extra"
+      "label3 value3 extra";
+  }
+}
+
+.user-name-heading { grid-area: heading; display: flex; align-items: center; gap: 0.4rem; flex-wrap: wrap; margin: 0 0 0.25rem 0; }
+.org-role-sub { grid-area: org; display:flex; flex-direction:column; margin: -0.15rem 0 0.25rem; }
 .org-line { font-size: .7rem; font-weight:600; line-height:1.1; color: var(--color-text-muted); text-transform: uppercase; letter-spacing: 0.05em; }
 .role-line { font-size:.65rem; color: var(--color-text-muted); line-height:1.1; }
-.user-info span { text-align: left; }
-.user-name-heading { display: flex; align-items: center; gap: 0.4rem; flex-wrap: wrap; margin: 0 0 0.25rem 0; }
+.info-label:nth-of-type(1) { grid-area: label1; }
+.info-value:nth-of-type(2) { grid-area: value1; }
+.info-label:nth-of-type(3) { grid-area: label2; }
+.info-value:nth-of-type(4) { grid-area: value2; }
+.info-label:nth-of-type(5) { grid-area: label3; }
+.info-value:nth-of-type(6) { grid-area: value3; }
+.user-info-extra { grid-area: extra; padding-left: 2rem; border-left: 1px solid var(--color-border); }
 .user-name-row { display: inline-flex; align-items: center; gap: 0.35rem; max-width: 100%; }
 .user-name-row.editing { flex: 1 1 auto; }
 .icon { flex: 0 0 auto; }
@@ -62,5 +102,6 @@ const userLoaded = computed(() => !!props.name)
 .mini-btn:hover:not(:disabled) { background: var(--color-accent-soft); color: var(--color-accent); }
 .mini-btn:active:not(:disabled) { transform: translateY(1px); }
 .mini-btn:disabled { opacity: 0.5; cursor: not-allowed; }
+@media (max-width: 768px) { .user-info-extra { padding-left: 0; padding-top: 1rem; border-left: none; border-top: 1px solid var(--color-border); } }
 @media (max-width: 480px) { .user-name-heading { flex-direction: column; align-items: flex-start; } .user-name-row.editing { width: 100%; } .display-name { max-width: 100%; } }
 </style>