Support min/max ranges for note mappings #116

Split out from #36.

Ranges now work for CC mappings in both directions: ["control_change", channel, controller, min, max] scales output into [min, max], and on input clamps and maps back to 0–1 (#105, #104). Note mappings don't support ranges yet.

The main use case is limiting the pitch range of note output, e.g. keeping a melody inside two octaves, or a drum machine that only responds to a few notes. On input, the same range would map a small keyboard or pad controller onto the full 0–1 dimension.

Format needs care, since ["note_on", channel, velocity] already means a fixed output velocity (#108). One option that parallels CCs is ["note_on", channel, velocity, min, max], with the same behaviour as ranged CCs:

• Output: round(min + value * (max - min)).
• Input: clamp the note to [min, max], then (note - min) / (max - min), with min == max giving 0.

Config changes should be careful here: docs/config.md, the example configs, the conformance vectors and impsy-auv3/impsy-web all need to agree.