Browse the knowledge base from a single side panel menu

Add a read-only view of backend/knowledge_base/**.md so the files that get
injected into the system prompt can be inspected from the GUI:

- GET /api/kb/files lists the Markdown files (title, preview, size, mtime and
  whether the file is already embedded), GET /api/kb/file returns one in full.
  Paths are resolved against the knowledge base directory and rejected unless
  they stay inside it and end in .md.
- KnowledgeBasePanel.vue groups the files by folder (collapsible, so web_search
  can be folded away), filters by title/path/preview and renders the selected
  file with MarkdownContent.

The header had grown to four side panel toggles, so collapse them into one
menu: panels.ts now holds the list of panels along with the component each one
renders, App.vue picks it with <component :is>, and SidePanelMenu.vue shows the
active panel on its button. Re-picking the open panel (or "パネルを閉じる")
closes it; a click outside or Esc closes just the menu.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/App.vue

@@ -1,27 +1,23 @@
 <script setup lang="ts">
-import { onMounted, onUnmounted, ref } from 'vue'
+import { computed, onMounted, onUnmounted, ref } from 'vue'
 import SessionList from './components/SessionList.vue'
 import ChatWindow from './components/ChatWindow.vue'
 import MessageInput from './components/MessageInput.vue'
 import ModelSelector from './components/ModelSelector.vue'
-import LogViewer from './components/LogViewer.vue'
-import SettingsPanel from './components/SettingsPanel.vue'
-import NotePanel from './components/NotePanel.vue'
+import SidePanelMenu from './components/SidePanelMenu.vue'
 import ToastList from './components/ToastList.vue'
 import MemoryMonitor from './components/MemoryMonitor.vue'
 import Clock from './components/Clock.vue'
 import WordPool from './components/WordPool.vue'
 import LoginGate from './components/LoginGate.vue'
+import { SIDE_PANELS, type PanelId } from './panels'
 import { useAuthStore } from './stores/auth'
 
 const authStore = useAuthStore()
 
-type SidePanel = 'none' | 'logs' | 'settings' | 'notes'
-const activePanel = ref<SidePanel>('none')
-
-function togglePanel(panel: SidePanel) {
-  activePanel.value = activePanel.value === panel ? 'none' : panel
-}
+/** 右サイドに開いているパネル。null はどれも開いていない状態。 */
+const activePanel = ref<PanelId | null>(null)
+const activePanelDef = computed(() => SIDE_PANELS.find((p) => p.id === activePanel.value) ?? null)
 
 function handleUnauthorized() {
   authStore.markUnauthenticated()
@@ -51,32 +47,20 @@ onUnmounted(() => {
           <span class="title">PlayChat</span>
           <ModelSelector />
           <Clock />
-          <button class="log-toggle" :class="{ active: activePanel === 'notes' }" @click="togglePanel('notes')">
-            ノート
-          </button>
-          <button class="log-toggle" :class="{ active: activePanel === 'settings' }" @click="togglePanel('settings')">
-            設定
-          </button>
-          <button class="log-toggle" :class="{ active: activePanel === 'logs' }" @click="togglePanel('logs')">
-            ログ
-          </button>
-          <button v-if="authStore.required" class="log-toggle" @click="authStore.logout()">
-            ログアウト
-          </button>
+          <div class="header-actions">
+            <SidePanelMenu :active="activePanel" @select="activePanel = $event" />
+            <button v-if="authStore.required" class="log-toggle" @click="authStore.logout()">
+              ログアウト
+            </button>
+          </div>
         </header>
         <div class="body">
           <div class="chat-pane">
             <ChatWindow />
             <MessageInput />
           </div>
-          <div v-if="activePanel === 'logs'" class="log-pane">
-            <LogViewer />
-          </div>
-          <div v-else-if="activePanel === 'settings'" class="log-pane">
-            <SettingsPanel />
-          </div>
-          <div v-else-if="activePanel === 'notes'" class="log-pane">
-            <NotePanel />
+          <div v-if="activePanelDef" class="log-pane">
+            <component :is="activePanelDef.component" />
           </div>
         </div>
       </div>
@@ -101,11 +85,11 @@ header {
   border-bottom: 1px solid #333; background: #1a1a1a; flex-shrink: 0;
 }
 .title { font-size: 16px; font-weight: 600; color: #fff; }
+.header-actions { display: flex; align-items: center; gap: 8px; }
 .log-toggle {
   background: #2a2a2a; color: #aaa; border: 1px solid #444;
   border-radius: 6px; padding: 4px 14px; font-size: 13px; cursor: pointer;
 }
-.log-toggle.active { background: #1d3557; color: #93c5fd; border-color: #2563eb; }
 .body { flex: 1; display: flex; overflow: hidden; }
 .chat-pane { flex: 1; display: flex; flex-direction: column; overflow: hidden; }
 .log-pane { width: 400px; min-width: 300px; border-left: 1px solid #2a2a2a; overflow: hidden; }