Internet Archive mirroring for KSA mods

[Maximilian-Nesslauer]

Goal

Decide and prepare Internet Archive mirroring for redistributable KSA mods, the same fallback the bot provides for KSP1.
KSA-CKAN-meta/repositories.json already carries "x_mirror": false with a comment saying it flips to true once mirroring is set up.

Findings (verified in this repo's source)

• IA collections are per-game free-form args (ia_collections, name=collection pairs) resolved via Game.ia_collection, so config-wise KSA is one more arg.
• BUT the Mirrorer service is currently instantiated with common.game('ksp').ia_collection (netkan/cli/services.py), i.e. production mirroring is effectively KSP1-only today; KSP2 apparently never got its own collection wired either.

Tasks

• Ask the CKAN team whether they want per-game mirroring generalized (KSP2 precedent suggests this was consciously deferred) or KSA deferred the same way.
• If yes: create/request an archive.org collection for KSA mods, add ksa=<collection> to the ia_collections config in prod-stack.py, and extend the mirror service to cover multiple games.
• After it is live: flip x_mirror to true in KSA-CKAN-meta's repositories.json.

Gate / sequencing

Depends on the bot indexing KSA at all (#1 here) and on a CKAN-team decision plus archive.org setup, so this is a post-upstream-merge follow-up, tracked now so it is not forgotten.

Part of KSP-CKAN/CKAN#4457.