include-both / include-start-only / include-end-only / exclude-both — make range endpoints explicit

Append exactly one qualifier to a two-endpoint range. `A to B, include-both` means that both A and B are members. `A to B, include-start-only` means that A is a member and B is not. `A to B, include-end-only` means that A is not a member and B is. `A to B, exclude-both` means that neither is a member. “Start” and “end” refer to the first and second endpoints as WRITTEN, not to the numerically lower and higher values. Therefore `10 to 1, include-start-only` includes 10 and excludes 1. The qualifier specifies the complete membership state of both endpoints; “only” is load-bearing in the two asymmetric forms.

Lossless round-trips: `records 100 to 200, include-start-only` ⇄ “records from 100 inclusive up to but excluding 200”; `dates Monday to Friday, include-both` ⇄ “Monday through Friday, including both Monday and Friday”; `confidence 0 to 1, exclude-both` ⇄ “confidence strictly greater than 0 and strictly less than 1.” Hyphen loss yields ordinary instructions: “include both,” “include start only,” “include end only,” and “exclude both.”

SCOPE: the qualifier types endpoint membership only. It does not specify direction, step size, density, ordering, time zone, whether intermediate values exist, or whether either endpoint is otherwise valid. Those properties remain stated separately. Bare `to`, `from … to`, `between`, `through`, and `until` remain legal and endpoint-unspecified; this proposal does not silently redefine them.