feat(workshop): add Steam Workshop downloads for Squad 44 and Operation: Harsh Doorstop

[dgibbs64]

Description

Extends the Workshop downloader (#5008, #5009) to Squad 44 and Operation: Harsh Doorstop. Neither dedicated server downloads Workshop mods itself. Both download anonymously, so no Steam account is needed.

Per-game install

• Squad 44: installs to PostScriptum/Plugins/Mods/<id>, the same as Squad. The server mounts every mod in that folder.
• Operation: Harsh Doorstop: installs to HarshDoorstop/Mods/<plugin folder> (for example Mods/TF_MODERN). OHD checks that a mod's pak is mounted from Mods/<plugin name>/. A mod left inside its Workshop ID folder fails with Plugin_PAK_Mount_Point_Unsupported, so a mod that is a single plugin folder is installed as that folder.
  • Mod maps and modes are selected with defaultmap or startparameters, as before.
  • If a folder with that name already exists and wasn't installed by LinuxGSM, the install is refused rather than overwriting it.

Other changes

• Each mod's .lgsm-workshop state file now records its Workshop id. Installed mods are looked up by that ID, so the folder name no longer has to be the ID.

Testing

Live test servers, running this branch:

• Operation: Harsh Doorstop (workshopmods="3131976970", TF_MODERN): installed to Mods/TF_MODERN, and the server log shows UGC 'TF_MODERN' loaded successfully. Ending state: Active. In the old nested layout, the same mod failed with Plugin_PAK_Mount_Point_Unsupported.
• Squad 44 (workshopmods="3600802863", Mos Teutonicus: Gun Game): the server log shows Successfully mounted and serialised mod: MT_GG from Plugins/Mods/3600802863.
  • Note: a Linux Squad 44 server only loads mods whose authors ship a LinuxNoEditor build. Two Windows-only mods tested were rejected by the game as invalid, in both layouts. That depends on the mod author, not LinuxGSM. Of six recently updated Squad 44 mods, three had a Linux build.
• Removal: clearing workshopmods removed the mods on both servers. Both servers stayed healthy and were restored afterwards.
• Locally:
  • The OHD install, re-run (no update reported) and removal all work.
  • A hand-made mod folder is never touched, and a name clash is refused.
  • Arma 3's @<id> layout is unchanged.
• shellcheck and prettier pass.

Type of change

• Bug fix (a change which fixes an issue).
• New feature (a change which adds functionality).
• New Server (new server added).
• Refactor (restructures existing code).
• Comment update (typo, spelling, explanation, examples, etc).

Checklist

• This pull request links to an issue.
• This pull request uses the develop branch as its base.
• This pull request subject follows the Conventional Commits standard.
• This code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have checked that this code is commented where required.
• I have provided a detailed enough description of this PR.
• I have checked if documentation needs updating.

Relates to #3514.

Documentation

Covered in GameServerManagers/LinuxGSM-Docs#132.

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