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.

crates/ailang-core/src/workspace.rs

@@ -1780,10 +1780,11 @@ mod tests {
 
     /// Iter 22b.1: an instance that omits a required (non-default)
     /// method of its class fires `MissingMethod`. The fixture's
-    /// `class TEq` declares `teq` and `ne` as both non-default; the
-    /// instance only specifies `ne`, leaving `teq` missing.
-    /// (Class is `TEq` rather than `Eq` to avoid colliding with the
-    /// auto-loaded prelude's `class Eq`.)
+    /// `class TEq` declares `teq` and `tne` as both non-default; the
+    /// instance only specifies `tne`, leaving `teq` missing.
+    /// (Class is `TEq` (and method `tne`) rather than `Eq` / `ne` to
+    /// avoid colliding with the auto-loaded prelude's `class Eq` and
+    /// — since iter 23.5 — the prelude's polymorphic free fn `ne`.)
     #[test]
     fn iter22b1_missing_method_fires_diagnostic() {
         let entry = examples_dir().join("test_22b1_missing_method.ail.json");