feat: add token auth, login page, skill toggle, and route restructure

- Add token-based authentication with auto-generated token stored in server/data/.token
- Add login page with URL token auto-fill support
- Add route guards requiring auth for all pages except login
- Restructure routes: / for login, /chat for conversations
- Add skill enable/disable toggle via config.yaml skills.disabled
- Unify logo to /logo.png across sidebar, login, messages, and empty state
- Hide sidebar on login page, prevent flash with router.isReady()
- Fix session export JSON parse error when CLI returns non-JSON output
- Display token in CLI on server start

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

src/components/chat/MessageItem.vue

@@ -124,7 +124,7 @@ const formattedToolResult = computed(() => {
       <div class="msg-body">
         <img
           v-if="message.role === 'assistant'"
-          src="/assets/logo.png"
+          src="/logo.png"
           alt="Hermes"
           class="msg-avatar"
         />