Bare numeric Discord IDs (e.g. '1470130713209602050') in cron
delivery.to caused 'Ambiguous Discord recipient' errors and silent
delivery failures.
Adds normalizeDiscordOutboundTarget() to the existing Discord
normalize module (channels/plugins/normalize/discord.ts) alongside
normalizeDiscordMessagingTarget. Defaults bare numeric IDs to
'channel:<id>', matching existing behavior.
Both the Discord extension plugin and standalone outbound adapter
use the shared helper via a one-liner resolveTarget.
Fixes#14753. Related: #13927
3238bd78d9