preset-identity-read-back-from-value

Derive "which preset is this" by comparing the presets against the value in force instead of storing a label beside it, so editing drops to Custom by itself and returning re-selects — and derive any per-preset field that is a function of the preset's own numbers rather than writing it out per row. Use when a preset picker keeps showing a stale name, when a preset never re-selects itself, or when a per-row constant…