Improve resilience with connectivity issues

[Betree]

We had various reports of disconnect not being appropriately handled, which can produce different results:

• The person tries to add a comment; it is effectively added but never appears in the interface
• We show a random "disconnected" message, and it's unclear whether we missed any API event. This likely happens after putting the tab in the background for a few minutes.

To reproduce:

• Open a video
• Set yourself as "Offline" in the network settings
• Re-connect
• Try to post a comment

Expected:

• Users should be reconnected to the channel
• We should fully re-synchronize the state in case we missed any event
• All form states should be preserved (do not erase pending comments)
• We can eventually show a loading status with all fields disabled while reconnecting
• Once reconnected, a "Success - Reconnected" toast should pop up