[golden] Golden fixtures are weaker than their documented pass criteria (GS-4/5/6/7/9/10/11/13)

[JArmandoAnaya]

What

Several golden fixtures are weaker than the pass criteria docs/roadmap/golden-scenarios.md declares for them, so the acceptance suite does not test what the release doc says it tests:

GS	Declared	Fixture reality
GS-4	TimeToCollision trigger + min-gap/no-collision checkpoint	distance keeping triggered by SimulationTimeCondition value="1"; only two speed checkpoints
GS-5	polyline pedestrian trajectory, TTC brake, ReachPosition resume	no Trajectory element; constant-speed pedestrian; ego brakes on SimulationTimeCondition value="4"; no resume
GS-6	TTC trigger, StandStillCondition, non-zero ConditionDelay	two SimulationTimeConditions, delay="0" throughout
GS-7	polyline + clothoid + NURBS chained with TimeReference	Polyline only, <TimeReference><None/> (clothoid/NURBS live only in determinism_test.cpp)
GS-9	catalog + ParameterAssignments, second overridden run, malformed variant asserting a rule-ID diagnostic	expressions only; tests/golden/catalogs/ declared in the layout but absent; harness has no override path
GS-10	scena-run --replay ego=<csv> host round-trip	run_scenario() never passes --replay; no replay CSV committed; the Controller source=host property is consumed by no code — checkpoint comes from an engine-side SpeedAction
GS-11	junction map + cross-vehicle-during-orthogonal-phase checkpoint	signals only, no map, no cross-vehicle checkpoint
GS-13	"--select brake changes what runs and nothing else"	golden.py Scenario has no select field; only the default alternative ever runs in CI

Harness gaps: golden.py has no compare-external subcommand though golden-scenarios.md:39 documents --compare-external <trace> --tol <spec>.

Done when

• Each fixture upgraded to its declared criteria (or the doc criteria amended where a deliberate simplification is kept — decision recorded per scenario)
• golden.py Scenario gains replay and select fields; GS-10 exercises --replay, GS-13's --select arm runs in CI with its own reference trace
• Decide whether an XML Controller property source=host should map to host control ownership; today it is decorative
• compare-external implemented or the doc downgraded to "maintainer-run, ad hoc"