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>

tools/x/tools.ludic

@@ -178,6 +178,10 @@ function cmd_test_tools() -> int {
   # Ported to Ludic; runs through x.
   if shq("bin/x check-impl > /dev/null 2>&1") { ok("docs cover every implemented feature") } else { bad("docs drifted from the implementation") }
 
+  # every ```ludic fence in the docs must parse (or be marked skip/expect-error),
+  # so a documented snippet can't drift from what the compiler accepts.
+  if shq("bin/x check-docs > /dev/null 2>&1") { ok("every doc fence parses") } else { bad2("a doc fence drifted", "run: x check-docs") }
+
   return report()
 }