Add auto-updating support for Steam Workshop mods

[JnCaoxia]

Closes #215 — adds auto-updating support for Steam Workshop mods (e.g. DayZ server mods).

Note: This PR builds upon the earlier work in #280 (derived PR as described in BOUNTY_TERMS §6). The original PR was closed by its author; this implementation addresses all remaining review feedback on top of the current master.

What changed

• Discovery: SteamWorkshopMod scans the mods folder for directories containing meta.cpp and reads publishedid, name and timestamp.

• Update check: New SteamWorkshopUpdateFinder (same per-task usage pattern as ResourceFinder) queries the Steam Web API (GetPublishedFileDetails) and only reports UPDATE_AVAILABLE when time_updated is newer than the version cached in mods.yml — mods are not re-downloaded on every run.

• Download: New TaskSteamWorkshopModDownload (mirrors TaskModDownload) downloads the item via SteamCMD workshop_download_item, honoring NOTIFY / MANUAL / AUTOMATIC profiles; with AUTOMATIC the content is copied back into the existing mod directory and the cached version is updated.

• Config: steam-workshop-id is cached in mods.yml; mods-updater.path and the mods.yml header comments document the feature. The existing server-updater.software setting is reused as the Steam app-id (e.g. 221100 for DayZ) — no new config key needed.

Review feedback from #280 addressed

• Update-check logic extracted into its own class (SteamWorkshopUpdateFinder), used like ResourceFinder, and integrated into the existing parallel executor instead of a separate flow.

• The version no longer defaults to the publishedId (the confusing line in Add DayZ workshop mod updates #280): a Workshop mod's version is its meta.cpp timestamp when present, otherwise empty, so the first update check always runs.

• Update check only marks UPDATE_AVAILABLE when the item actually changed (compares time_updated against the cached version).

• Download logic integrated into doDownloadLogic via TaskSteamWorkshopModDownload, following the TaskModDownload pattern; both share the new ModDownloadTask interface.

• A test showing the actual update process: see end-to-end tests below.

Note on the Steam Web API call

GetPublishedFileDetails only accepts POST form requests — GET returns an error (verified against the live API). Since jlib's Json.get(url) performs a GET, it cannot be used here. The implementation uses a plain HttpURLConnection POST plus the already-present Gson dependency, so no new dependencies are introduced (per BOUNTY_TERMS §5).

Testing

• mvn -DskipTests compile — clean (OpenJDK 17, release 9 target)

• mvn -Dtest='SteamWorkshopModTest,SteamCMDTest#buildsWorkshopItemCommand' test — 5/5 green:

  • meta.cpp parsing (id / name / timestamp)

  • Workshop mod discovery in the mods folder

  • E2E: metadata current → no download, no warnings, version kept

  • E2E: newer metadata → SteamCMD download → files copied into the mod dir → new version cached in mods.yml

  • SteamCMD workshop command building

AI-assisted contribution disclosure

Per BOUNTY_TERMS §4: this contribution was developed with AI assistance. All code has been reviewed line-by-line, compiled, and tested locally by me, and I take full responsibility for its behavior and quality.

Payment: my PayPal email is visible on my public GitHub profile (per BOUNTY_TERMS §2).