schema: ludicc --emit-schema / ludic schema, --check --diagnostics=json, and editor attributes

--emit-schema FILE writes the compiler's resolved view once the program type-checks: every
record (fields, types, defaults as written, docs, places, attributes), every registry with its
entries in their final order after the open-registry merge (key, constant, index, file:line:col
of the entry and of each field value, and which file contributed which keys), every const, and
the zero-argument functions a fn value can name. Deterministic, schema_version 1; the runtime is
left out. `ludic schema [file] [-o FILE]` wraps it.

--check --diagnostics=json prints every error as one JSON array on stdout: the checker's and the
module rules' all, a parse or lowering error as the last. Tokens and nodes now carry a column.

Fields take several @attributes; @Ref(Registry), @OneOf(PREFIX_), @Range(lo, hi), @Unit("..."),
@Asset("..."), @Color on a field and @AppendOnly / @ByKey on a registry change nothing but go into
the schema, and @Ref naming no registry is an error (every one reported). Fixtures:
examples/lang/attributes.ludic, examples/rejected/ref_unknown.ludic, cases in ludic-dev test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/check/check_env.ludic

@@ -41,9 +41,16 @@ function ck_reporting() -> bool {
 function ck_err(cat: pointer, n: Node, msg: pointer) -> void {
   var file: pointer = ""
   var line = 0
+  var col = 0
   if n != null {
     if n.file != null { file = n.file }
     line = n.line
+    col = n.col
+  }
+  if g_diag_json and not ck_reporting() {
+    diag_add(file, line, col, "error", msg)
+    ck_errors += 1
+    return
   }
   var m = `{file}:{itoa(line)}: error: {msg}\n`
   if ck_reporting() { m = `check[{cat}]: {file}:{itoa(line)}: {msg}\n` }