Add settings page, model management, and chat UX improvements

- Settings infrastructure: key-value settings table, GET/PUT API, Pinia store
- Configurable assistant name (default "Fable") in settings and LLM system prompt
- Model catalog with 18 models in 3 categories (General Purpose, Coding,
  Uncensored / Creative Writing) with download/select/remove functionality
- Move Ollama status indicator from chat views to global nav bar
- Chat bubble layout: user messages right-aligned, assistant left-aligned
- Floating dark input bar with auto-focus and circular send button
- Fix HTML entity rendering (' apostrophe issue in marked/DOMPurify pipeline)
- Fix new chat button navigation (fetchConversation before router.push)
- Recent chats section on home page with "New Chat" button
- Update summary.md with Phase 4.5 changes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/AppHeader.vue

@@ -1,11 +1,28 @@
 <script setup lang="ts">
+import { computed } from "vue";
 import { useTheme } from "@/composables/useTheme";
+import { useChatStore } from "@/stores/chat";
 
 const { theme, toggleTheme } = useTheme();
+const chatStore = useChatStore();
 
 const emit = defineEmits<{
   toggleChatPanel: [];
 }>();
+
+const statusLabel = computed(() => {
+  if (chatStore.ollamaStatus === "unavailable") return "Ollama unavailable";
+  if (chatStore.modelStatus === "not_found") return "Model downloading...";
+  if (chatStore.chatReady) return "Connected";
+  return "Checking...";
+});
+
+const statusClass = computed(() => {
+  if (chatStore.ollamaStatus === "unavailable") return "status-red";
+  if (chatStore.modelStatus === "not_found") return "status-yellow";
+  if (chatStore.chatReady) return "status-green";
+  return "status-yellow";
+});
 </script>
 
 <template>
@@ -16,6 +33,10 @@ const emit = defineEmits<{
         <router-link to="/notes" class="nav-link">Notes</router-link>
         <router-link to="/tasks" class="nav-link">Tasks</router-link>
         <router-link to="/chat" class="nav-link">Chat</router-link>
+        <router-link to="/settings" class="nav-link">Settings</router-link>
+        <span class="status-indicator" :class="statusClass" :title="statusLabel">
+          <span class="status-dot"></span>
+        </span>
         <button class="btn-chat-panel" @click="emit('toggleChatPanel')" title="Open chat panel">
           &#x1F4AC;
         </button>
@@ -59,6 +80,30 @@ const emit = defineEmits<{
 .nav-link:hover {
   color: var(--color-primary);
 }
+.status-indicator {
+  display: flex;
+  align-items: center;
+}
+.status-dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  flex-shrink: 0;
+}
+.status-green .status-dot {
+  background: #22c55e;
+}
+.status-yellow .status-dot {
+  background: #eab308;
+  animation: pulse-dot 2s infinite;
+}
+.status-red .status-dot {
+  background: #ef4444;
+}
+@keyframes pulse-dot {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.4; }
+}
 .btn-chat-panel {
   background: none;
   border: 1px solid var(--color-border);