iter 23.5: prelude free fns + E2E — Eq/Ord milestone close

Five polymorphic prelude free fns (ne/lt/le/gt/ge) plus three E2E
fixtures: positive composition over Int/Bool/Str, user-ADT with
user-written Eq/Ord on IntBox, and Float-NoInstance with a
Float-aware diagnostic addendum cross-referencing DESIGN.md §"Float
semantics".

Two checker-side fixes were needed alongside the prelude additions,
both symmetric to the iter 23.4-prep visibility fix:
- linearity::check_module_with_visible — workspace-aware callee-mode
  resolution so a Borrow-mode user fn forwarding into a prelude poly
  fn (e.g. `at_most x y = not (gt x y)`) doesn't false-fire
  consume-while-borrowed.
- mono::collect_mono_targets — distinguish rigid forall vars from
  unbound metavars; rigid-bearing free-fn targets skip (they get
  re-collected with concrete subst when the enclosing fn itself
  monomorphises). Without this, a polymorphic body calling another
  polymorphic free fn produced a spurious __Unit specialisation
  whose body referenced compare at Unit.

Roadmap split: shipped Eq/Ord half checked, Show + print-rewire half
remains pending behind the heap-Str ABI prerequisite. DESIGN.md
§"Prelude classes" amended.

One pre-existing fixture (test_22b1_missing_method) renamed its
class method ne → tne to avoid collision with the new prelude `ne`.

Bench: check.py + cross_lang.py exit 0; compile_check.py exits 1
with one sub-ms check_ms.local_rec_capture at +26% (tolerance 25%) —
prelude-growth-related noise-band fluctuation, ratifiable per spec
§248-249 and journal Concerns.

docs/DESIGN.md

@@ -1701,6 +1701,16 @@ end-to-end path is the milestone's typeclass acceptance gate
 `instance Foo IntBox`); see `docs/specs/2026-05-09-22-typeclasses.md`
 "Amendments" for the substantive rationale.
 
+Milestone 23 amends the above: the prelude now ships the `Ordering`
+ADT, the `Eq` and `Ord` classes, primitive `Eq Int/Bool/Str` and
+`Ord Int/Bool/Str` instances, and the five polymorphic free-fn helpers
+`ne` / `lt` / `le` / `gt` / `ge`. `Show`, operator routing through
+`Eq`/`Ord`, and `print`-rewire remain out of scope per their original
+substantive reasons (heap-`Str` ABI, bench rebaseline). Float has
+neither `Eq` nor `Ord` instance per §"Float semantics"; a polymorphic
+helper invoked at Float fires `NoInstance` at typecheck with a
+Float-aware diagnostic cross-referencing this section.
+
 Primitive output goes through `io/print_int` / `io/print_bool` /
 `io/print_str` directly.