[Priveetee]

Summary

• Show the video thumbnail in alerts, loaded through the server image proxy, with retries while YouTube still serves its processing placeholder.
• Badge the alert icon with the video platform.
• Prepare alerts before posting them, then post and record them in one step, so an interrupted poll no longer posts the same alerts twice.

Validation

• Android unit tests, lint and debug build passed.
• Physical device: YouTube alerts showed their real thumbnail; Bilibili thumbnails confirmed by the owner; no duplicate alerts across repeated polls.
• Not verified on a device: NicoNico thumbnails.