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/i18n/locales/en.ts

@@ -1,4 +1,15 @@
 export default {
+  // Login
+  login: {
+    title: 'Login',
+    description: 'Enter your access token to continue. Find it in the server startup logs.',
+    placeholder: 'Access token',
+    submit: 'Login',
+    tokenRequired: 'Please enter your access token',
+    invalidToken: 'Invalid token',
+    connectionFailed: 'Cannot connect to server',
+  },
+
   // Common
   common: {
     loading: 'Loading...',
@@ -133,6 +144,7 @@ export default {
     attachedFiles: 'Attached Files',
     loadFailed: 'Failed to load skill',
     fileLoadFailed: 'Failed to load file',
+    toggleFailed: 'Failed to toggle skill',
   },
 
   // Memory