fix(download): hook downloadDeleteEvent in BaseFetchButton to reset UI on cancel

[LeC-D]

Fixes #1227

Problem

When a download is cancelled from a notification, the download button UI (in episode list, result screen, etc.) is not updated. The button keeps showing a stale download state instead of resetting.

Root cause

downloadDeleteEvent was implemented as a stub in BaseFetchButton but the event subscription was commented out in onAttachedToWindow / onDetachedFromWindow, so the callback was never invoked.

Fix

• Implement downloadDeleteEvent(data: Int): when the deleted ID matches persistentId, call resetView() to bring the button back to its initial state.
• Subscribe to VideoDownloadManager.downloadDeleteEvent in onAttachedToWindow.
• Unsubscribe in onDetachedFromWindow to avoid memory leaks.

This pattern is identical to how downloadStatusEvent and downloadProgressEvent are already handled in the same class.

AI Usage Disclosure

This fix was developed with AI assistance (GitHub Copilot / Claude for context exploration), per the project's AI Policy. I am fully responsible for understanding and verifying the code. The approach directly mirrors existing patterns already in BaseFetchButton, and the change has been manually reviewed and tested.

[LeC-D]

Hi @fire-light42, thanks for pointing to the AI policy.

To be transparent: this fix was developed with AI assistance (GitHub Copilot / Claude for context exploration). I'm fully responsible for understanding and verifying the code — the approach directly mirrors the existing downloadStatusEvent and downloadProgressEvent patterns already in BaseFetchButton, so the change is straightforward and intentional. I've reviewed and tested the logic manually.

Let me know if you have any concerns about the implementation itself!

[LeC-D]

Updated the PR description to include the AI usage disclosure directly in the body, as required by the AI Policy. Thanks for flagging this, @fire-light42!

[LeC-D]

Rebased on upstream master (2026-04-03) to bring the branch back up to date.