source: scrub iter-code / Decision-N residue from inline comments

Follow-up to bcd4181: the remaining ~530 inline `//` and `///`
comments still carrying opaque shorthand are now reformulated to
their content phrases. The only surviving `iter-<code>` reference
in source is the literal filename
`docs/journals/2026-05-13-iter-mq.3.md` (a real journal file).

Sweep covered:
  - `// Iter X.Y: <text>` prefixes (Iter 13a / 14a / 14e / 15g-aux /
    16b.x / 16d / 16e / 18b / 18c.x / 18d.x / 18e / 18g.x / 19a /
    19a.1 / 19b / 20a / 20f / 22-floats.x / 22b.x / 22c / 23.x /
    24.1 / cli-diag-human / hs.x / str-concat / etc.) — fully
    removed; the descriptive text that followed each prefix stays.
  - `// (Decision N)` and `per Decision N` and `Decision N axis 3` —
    replaced with the content phrase plus the relevant contract
    file (`design/contracts/tail-calls.md` for Decision 8,
    `design/contracts/memory-model.md` for Decision 10,
    `design/contracts/typeclasses.md` and `design/models/typeclasses.md`
    for Decision 11, `design/contracts/authoring-surface.md` for
    Decision 6, "the transitional dual-allocator" for Decision 9,
    "Effect prose" for Decision 3).
  - `// mq.X / mq.X (Task N) / mq.X journal / mq.X invariant` ->
    "the canonical-class-form rule / Class-class repurpose /
    method-dispatch-refactor journal / canonical-class-form
    invariant".
  - `// ct.X / ct.X (canonical-type-names) / ct.1.5a + ctt.2 /
    ct.2 Task N` -> "the canonical-form rule for type references /
    the canonical-form normalisation step / canonical-type-lookup
    refactor".
  - `// eob.X` -> "heap-Str-ABI" / "the Str carve-out".
  - `// rpe.X` -> "the per-type-print-op retirement".
  - `// post-mq.X / Pre-ct.X / pre-mq.X` -> "post-canonical-class-form" /
    "Pre-canonical-type-form" etc.
  - `/// Iter X regression: / /// Iter X.Y: / /// Iter A arm-close /
    /// Iter ct.4 (...): / /// Iter rpe.1 ...` -> descriptive
    phrases.

The journal filename in `crates/ailang-core/src/workspace.rs:573`
stays verbatim because it points at an actual file under
`docs/journals/`.

Tests: full `cargo test --workspace` green (80/80 test-result blocks
clean, no FAILED line). design_index_pin 5/5 + docs_honesty_pin 5/5
gating tests pass.

crates/ailang-codegen/src/escape.rs

@@ -174,18 +174,18 @@ fn walk(t: &Term, out: &mut NonEscapeSet) {
             walk(body, out);
         }
         Term::LetRec { body, in_term, .. } => {
-            // Iter 16b.x: LetRec is normally eliminated before codegen.
+            // LetRec is normally eliminated before codegen.
             // Still walk for completeness.
             walk(body, out);
             walk(in_term, out);
         }
         Term::Clone { value } => {
-            // Iter 18c.1: clone is identity at IR level — only walk
+            // clone is identity at IR level — only walk
             // sub-terms looking for Let-allocation candidates.
             walk(value, out);
         }
         Term::ReuseAs { source, body } => {
-            // Iter 18d.1: identity at IR level (codegen lowers `body`,
+            // identity at IR level (codegen lowers `body`,
             // ignores `source`). Walk both children for completeness.
             walk(source, out);
             walk(body, out);
@@ -361,13 +361,13 @@ fn escapes(t: &Term, tainted: &BTreeSet<String>, in_tail: bool) -> bool {
             true
         }
         Term::Clone { value } => {
-            // Iter 18c.1: clone is identity. The wrapper's escape
+            // clone is identity. The wrapper's escape
             // verdict is exactly that of its inner term, threaded
             // through with the same `in_tail` context.
             escapes(value, tainted, in_tail)
         }
         Term::ReuseAs { source, body } => {
-            // Iter 18d.1: identity at IR level. The whole expression's
+            // identity at IR level. The whole expression's
             // value is `body`, so its escape verdict is the body's
             // (threaded through `in_tail`). The `source` is evaluated
             // but its value is discarded; it cannot escape via the
@@ -490,11 +490,11 @@ fn collect_free_vars(t: &Term, bound: &mut BTreeSet<String>, out: &mut BTreeSet<
             collect_free_vars(in_term, bound, out);
         }
         Term::Clone { value } => {
-            // Iter 18c.1: clone is identity for free-var collection.
+            // clone is identity for free-var collection.
             collect_free_vars(value, bound, out);
         }
         Term::ReuseAs { source, body } => {
-            // Iter 18d.1: free vars are the union of source and body.
+            // free vars are the union of source and body.
             collect_free_vars(source, bound, out);
             collect_free_vars(body, bound, out);
         }