feat: add admin REST API layer for frontend management panel

Implement JWT-protected /admin/* routes on the relay server:
- Auth: login, logout, me, setup/status, setup/init (first-time config)
- Dashboard: stats overview (connections, devices, cookies, domains)
- Cookies: paginated list with domain/search filter, detail, delete, batch delete
- Devices: list with online status, revoke
- Settings: get/update (sync interval, max devices, theme)

Uses scrypt for password hashing and jsonwebtoken for JWT.
Adds listAll/revoke to DeviceRegistry, getAll/getById/deleteById to CookieBlobStore,
disconnect to ConnectionManager. Updates frontend to use /admin/* endpoints.

All 38 existing tests pass.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

web/vite.config.ts

@@ -17,6 +17,10 @@ export default defineConfig({
         target: "http://localhost:8100",
         changeOrigin: true,
       },
+      "/admin": {
+        target: "http://localhost:8100",
+        changeOrigin: true,
+      },
       "/ws": {
         target: "ws://localhost:8100",
         ws: true,