std: the prelude becomes a pure re-export facade — implementations move to std/core.sx, std/fmt.sx, std/list.sx

std.sx now contains only alias declarations (the re-export mechanism:
own decls carry one flat-import level) over three part-files: core.sx
(builtins, libc escape hatch, Source_Location/Allocator/Context/Into,
the reserved `string` decl — which needs and permits no alias), fmt.sx
(print/format/any_to_string/string ops/cstring/alloc_slice), list.sx
(List). The namespace tail is unchanged; the part-file namespaces
(core/fmt/list) carry alongside it. Consumer surface is byte-identical
— every bare prelude name resolves through the aliases (0120/0121
machinery). 37 .ir snapshots re-pinned: pure string-constant
renumbering from the changed import graph (digit-normalized diff is
empty). Gates: zig build test 426/426, suite 588/588, m3te 23/23,
game SxChess builds + bundles.

readme.md

@@ -465,8 +465,11 @@ site.)
 **Namespace aliases carry one level.** A namespaced import is an ordinary
 declaration, and flat-importing the module that declares it makes the alias
 usable in the importer — there is no `pub` keyword. The stdlib prelude uses
-exactly this: `#import "modules/std.sx"` gives every bare prelude name
-(`print`, `List`, `Context`, …) plus the carried namespaces of std's tail
+exactly this: std.sx is itself a pure re-export facade (every bare prelude
+name is an alias into the `std/core.sx` / `std/fmt.sx` / `std/list.sx`
+part-files), and `#import "modules/std.sx"` gives every bare prelude name
+(`print`, `List`, `Context`, …) plus the carried namespaces — the
+part-files (`core`, `fmt`, `list`) and std's tail
 (`mem`, `fs`, `process`, `socket`, `json`, `cli`, `hash`, `xml`, `log`, `test`):
 
 ```sx