GLM-5.3 accepts a graded low/medium/high/max reasoning_effort scale
(verified live in #91789: monotonic reasoning-token scaling, no 400s),
but the effort mapper reused GLM-5.2's two-level vocabulary, silently
rewriting low/medium to high. Adds GLM53_EFFORTS/GLM53_OVERRIDES and a
per-model vocabulary pick in the zai plugin; 5.2 keeps its high/max
clamp. Closes#91789. Also covers the gap noted when closing #86947
(credit @santhanakrishnan-d and @terje1965 for the graded-scale finding).