feat(lang): new Type { field: value } record initialisers

`new` accepted only a bare `new T` (every field its declared default) or
`new []T`, but the docs (kw-new) document `new Record { field: value, … }`
as the way to construct a record with non-default fields — a documented,
intended form the parser never accepted (`let o = new Point { x: 3 }` failed
with "expected newline or ';'").

Parse an optional `{ … }` override record after the type in a `new`
expression (reusing the existing `record()` parser that `spawn` uses), and
seed each field in emit_new_struct from that record when present, else from
the field's declared default. `new []T` and bare `new T` are unchanged.

Also mark the illustrative kw-import fence `# doc-check: skip` (its imports
are example paths that can't resolve in isolation), which makes `x check-docs`
fully green (398 fences, 0 drifted) — so it is now wired as a gate in
`x test-tools` and CI, guarding against future doc/compiler drift.

Reseed is a clean fixpoint (x bootstrap-cfree holds); x test (56),
x selfhost-test (29, golden renders unchanged) and x test-tools (30) green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/backend/emit_call.ludic

@@ -407,7 +407,7 @@ function emit_expr(e: Node) -> Val {
   if e.kind == E_STR  { return val(emit_str_const(e.s), "string") }
   if e.kind == E_NEW  {
     if is_slice_ty(e.s) { return emit_new_slice(e.s) }
-    return emit_new_struct(e.s)
+    return emit_new_struct(e.s, e.a)
   }
   if e.kind == E_ID {
     let li = loc_find(e.s)

selfhost/backend/emit_new.ludic

@@ -7,7 +7,23 @@ function emit_sizeof(llt: pointer) -> pointer {
   return emit_bind(`ptrtoint ptr {p} to i64`)
 }
 
-function emit_new_struct(name: pointer) -> Val {
+# the value expression a `new T { ... }` record supplies for field `fname`,
+# or null when the record omits it (so the field keeps its declared default).
+function rec_field(rec: Node, fname: pointer) -> Node {
+  if (rec == null) { return null }
+  var i = 0
+  while i < len(rec.kids) {
+    let fi = rec.kids[i]
+    if (fi.s == fname) { return fi.a }
+    i = i + 1
+  }
+  return null
+}
+
+# `new T` / `new T { field: value, ... }` — allocate a record and seed each
+# field: a value from the override record if given, else the field's declared
+# default. `rec` is the E_REC of overrides (or null for the bare `new T`).
+function emit_new_struct(name: pointer, rec: Node) -> Val {
   let s = layout_node(name)                     # a struct or a property — same shape
   if (s == null) { perr("unknown record type in new") }
   let lty = layout_ty(name)
@@ -23,6 +39,8 @@ function emit_new_struct(name: pointer) -> Val {
     var v = "0"
     if (lt == "ptr") { v = "null" }
     if (fd.a != null) { let dv = emit_expr(fd.a);  v = dv.code }
+    let ov = rec_field(rec, fd.s)               # explicit override wins over the default
+    if (ov != null) { let dv = emit_expr(ov);  v = dv.code }
     emit("  store ");  emit(lt);  emit(" ");  emit(v);  emit(", ptr ");  emit(addr);  emit("\n")
     f = f + 1
   }