[Traking] offline mode

[HMarzban]

• display indicator showing online and offline status #72
• Document title change should be disabled when the document is offline
• When the application is offline, the user should not be able to create a new document that is not saved in the browser's storage(prevent content conflict)

[HMarzban]

Closing as tracking. Item 1 is done in #72. Item 3 holds by architecture: a pad needs SSR, and draft ids come from the slug. Item 2, the offline Pad title rename, is built: an offline rename now queues and says so, from the pad title and from Settings. The offline copy of the pad is hardened in #197.