iter prose-loop-binders.1: Form-B loop binders as parenthesised init-list

The Term::Loop arm of write_term rendered binders as bare
`name = init;` statements inside the `loop { … }` body block, which
reads as C/Rust re-init-every-iteration semantics — a projection
lying about a body the prose surface exists to let the reader trust.
Rewrite to a parenthesised init-list on the keyword line,
`loop(acc = 0, i = 1) { … }`, positionally isomorphic to the
unchanged Term::Recur arm. Projection-only: loop/recur AST, Form-A,
JSON-AST, typecheck, codegen, and the Form-A↔JSON round-trip
invariant untouched. RED-first via two new committed
examples/*.prose.txt byte-equality snapshots + two snapshot_loop_*
tests; full ailang-prose suite 10/0; both ail-prose CLI byte-matches
green. Single-iteration milestone, brainstorm→plan→implement.

Spec: docs/specs/2026-05-18-prose-loop-binders.md
Plan: docs/plans/prose-loop-binders.1.md

crates/ailang-prose/src/lib.rs

@@ -936,17 +936,16 @@ fn write_term_prec(out: &mut String, t: &Term, level: usize, parent_prec: u8, ow
             write_term(out, value, level, owning_module);
         }
         Term::Loop { binders, body } => {
-            // loop-recur iter 1: minimal-correctness Form-B render.
-            // Prose surface for loop is not yet designed; render the
-            // shape so a reader sees it without overcommitting.
-            out.push_str("loop {\n");
-            for b in binders {
-                indent(out, level + 1);
+            out.push_str("loop(");
+            for (i, b) in binders.iter().enumerate() {
+                if i > 0 {
+                    out.push_str(", ");
+                }
                 out.push_str(&b.name);
                 out.push_str(" = ");
-                write_term(out, &b.init, level + 1, owning_module);
-                out.push_str(";\n");
+                write_term(out, &b.init, level, owning_module);
             }
+            out.push_str(") {\n");
             indent(out, level + 1);
             write_term(out, body, level + 1, owning_module);
             out.push('\n');