check: over-strict-mode lint (iter 19a)

When a fn-param is annotated (own T) but the body never consumes
it (consume_count == 0) and never destructures it via match, the
linearity pass now emits a Severity::Warning diagnostic with a
form-A-rendered (borrow T) rewrite as suggested_rewrite. Pure
advisory, Decision 10 unchanged.

First Warning-severity diagnostic the typechecker emits; three
CLI exit paths gated on Error-only.

JOURNAL: design entry + iter 19a shipping entry.

crates/ailang-surface/src/lib.rs

@@ -36,4 +36,4 @@ pub mod parse;
 pub mod print;
 
 pub use parse::{parse, parse_term, ParseError};
-pub use print::{print, term_to_form_a};
+pub use print::{print, term_to_form_a, type_to_form_a};

crates/ailang-surface/src/print.rs

@@ -43,6 +43,16 @@ pub fn term_to_form_a(t: &Term) -> String {
     out
 }
 
+/// Iter 19a: render a [`Type`] as form-A. Used by diagnostics that want
+/// to suggest a relaxed signature (e.g. `over-strict-mode` shows the
+/// `(fn-type ...)` with `(borrow T)` in place of `(own T)`). Output is
+/// the same shape that appears as the `type` slot of a `(fn ...)` def.
+pub fn type_to_form_a(t: &Type) -> String {
+    let mut out = String::new();
+    write_type(&mut out, t);
+    out
+}
+
 // ---- helpers --------------------------------------------------------------
 
 fn indent(out: &mut String, level: usize) {