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-prose/src/lib.rs

@@ -89,7 +89,7 @@ fn write_def(out: &mut String, def: &Def, level: usize, owning_module: &str) {
     }
 }
 
-/// Iter 19b: render the [`FnDef::suppress`] list as one
+/// render the [`FnDef::suppress`] list as one
 /// `// @suppress <code>: <reason>` line per entry, indented to
 /// `level`. Multiple entries stack in declaration order; an empty
 /// list produces no output (and therefore no leading blank line).
@@ -233,7 +233,7 @@ fn write_ctor(out: &mut String, c: &Ctor, owning_module: &str) {
 }
 
 fn write_fn_def(out: &mut String, fd: &FnDef, level: usize, owning_module: &str) {
-    // Iter 19b: render `suppress` entries as `// @suppress <code>: <reason>`
+    // render `suppress` entries as `// @suppress <code>: <reason>`
     // comment lines **above** the doc string. They are contract metadata
     // that the LLM-reader needs to see to understand why an annotation
     // that looks over-strict is correct here. One line per entry, in
@@ -1783,7 +1783,7 @@ mod tests {
         assert!(out.contains("() -> Unit with IO {"), "got:\n{out}");
     }
 
-    /// Iter 19b: a FnDef with a single `Suppress` entry renders the
+    /// a FnDef with a single `Suppress` entry renders the
     /// `// @suppress <code>: <reason>` line **above** the doc string,
     /// preserving both the suppression visibility and the doc content.
     /// The suppress line must appear before the `///`-prefixed doc
@@ -1829,7 +1829,7 @@ mod tests {
         );
     }
 
-    /// Iter 19b: multiple `Suppress` entries render as one
+    /// multiple `Suppress` entries render as one
     /// `// @suppress <code>: <reason>` line each, in declaration
     /// order, all above the doc string.
     #[test]
@@ -1860,7 +1860,7 @@ mod tests {
         // Order: declaration order is preserved.
     }
 
-    /// Iter 19b: a FnDef with an empty `suppress` Vec emits no
+    /// a FnDef with an empty `suppress` Vec emits no
     /// `// @suppress` line at all (and therefore no extra leading
     /// blank line). Pre-19b prose snapshots stay byte-identical when
     /// re-rendered through the 19b code.
@@ -1928,7 +1928,7 @@ mod tests {
     }
 
     // ======================================================================
-    // Iter 20b: formatting polish
+    // formatting polish
     // ======================================================================
 
     /// Convenience: two-arg App of a named callee. Used pervasively in