uSync: v17→v18 forward port, prerelease workflow rename

Repo: KevinJump/uSync

Forward-ported v17's configurable bad-filename blocklist (AdditionalBadNames/ IncludeWindowsReservedNames on uSyncSettings) into v18/main via #1086
Renamed v18's package-build.yml to prerelease.yml and switched it to a manual workflow_dispatch trigger only, referencing v17's #1082 — #1087
Reviewed the same bad-filename-blocklist change on #1085 (v17/main) and #1084 (v13/dev) — both mergeable, no blockers