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/api/skills.ts

@@ -3,6 +3,7 @@ import { request } from './client'
 export interface SkillInfo {
   name: string
   description: string
+  enabled?: boolean
 }
 
 export interface SkillCategory {
@@ -53,3 +54,10 @@ export async function saveMemory(section: 'memory' | 'user', content: string): P
     body: JSON.stringify({ section, content }),
   })
 }
+
+export async function toggleSkill(name: string, enabled: boolean): Promise<void> {
+  await request('/api/skills/toggle', {
+    method: 'PUT',
+    body: JSON.stringify({ name, enabled }),
+  })
+}