japanese/proxy2ch: Update to 20260306-snapshot

The domain for 5Channel has changed from 5ch.net to 5ch.io.
Since data acquisition is no longer possible in the release version,
update to a snapshot.
The proxy2ch_flags in rc.d/proxy2ch wasn't working, so change it to
proxy2ch_args.

Changelog (japanese):
https://codeberg.org/NanashiNoGombe/proxy2ch/releases/tag/v20260306-snapshot

PR: 294108
Approved by: fluffy (mentor)