docs: add unit and range documentation to message fields

[youtalk]

Description

Add documentation comments to message fields to clarify units, ranges, and valid values.

Currently, many message fields lack documentation about:

• Units (e.g., m/s, rad, %)
• Valid ranges (e.g., 0.0-1.0, >= 0.0)
• Valid constant values for enum-like fields

Purpose

• Improve API clarity and reduce ambiguity
• Help developers understand expected input/output values
• Reduce integration errors caused by incorrect value ranges

Possible approaches

Add inline comments to .msg files following the pattern:

# Description [unit]. Range: min to max
field_type field_name

Definition of done

• All numeric fields have unit documentation where applicable
• All normalized values (0.0-1.0) have range documentation
• All enum-like fields reference their valid constants