Replace fixture player ids with POST …/__dev/mastery-fixture (resetPerkState,
absolute skillXp). Bruno deny tests set state in pre-request on dev-local-1.
Gated to Development/Testing or Game:EnableMasteryFixtureApi.
Seed neo48-perk-fresh and neo48-perk-branch via Game:FixturePlayerIds;
level_too_low uses isolated fresh player, branch_already_chosen sets up
neo48-perk-branch in pre-request instead of skipping on shared state.
Add self-contained branch_already_chosen Bruno request, HTTP deny smoke
for unknown track/tier/branch and null-body 400, folder docs for level_too_low.