bug: map rotation review fixes

[lukepolo]

Fixes from the review of #464.

• Dedicated server rebuilds run one at a time per server; overlapping saves could delete the deployment the other had just created
• A map deleted after the page loaded is dropped from the rotation instead of blocking every save
• Workshop import only takes items tagged Map (not skins or collections) and restores a deleted map disabled and out of the seed pools
• Rotation maps sharing a display name get distinct MapChooser names (it changes map by name)
• Rotation config merges over a game mode's config for the same file instead of replacing it
• A workshop start map boots +map de_dust2 ... +host_workshop_map <id>; without the stock map CS2 never logs on to Steam and sits idle with no RCON (verified live: loads prophunt_office)
• server_map_rotation is admin-only

Merge/deploy: metadata apply. Includes a codegen commit.
Tests: 5 unit + 5 SQL regressions fail on main and pass here.