std: restructure — std/ modules, namespace tail, std/xml.sx

allocators/fs/process/socket/log/trace/test move under modules/std/
(allocators.sx becomes std/mem.sx; the Allocator protocol moves into
the std.sx prelude, impls stay in mem.sx). New std/xml.sx holds
xml_escape as xml.escape. std.sx gains the carried namespace tail —
flat-importing std.sx now also provides mem./xml./log. — with the
remaining modules (fs/process/socket/json/cli/hash/test) deferred from
the tail until the global last-wins maps are fully own-wins (pulling
them into every closure collides bare names corpus-wide; they stay
direct imports: modules/std/fs.sx etc.). log.sx's internal emit
renamed log_emit (it clobbered consumer fns named emit program-wide).
bundle.sx uses xml.escape via the carried alias. Consumer import paths
swept mechanically; .ir snapshots recaptured for the larger std
closure. m3te + game build unchanged.

library/modules/std/socket.sx

@@ -0,0 +1,33 @@
+// POSIX socket module (macOS only)
+// sockaddr_in layout and constants are platform-specific.
+
+libc :: #library "c";
+
+// POSIX socket API
+socket     :: (domain: s32, kind: s32, protocol: s32) -> s32 #foreign libc;
+setsockopt :: (fd: s32, level: s32, optname: s32, optval: *s32, optlen: u32) -> s32 #foreign libc;
+bind       :: (fd: s32, addr: *SockAddr, addrlen: u32) -> s32 #foreign libc;
+listen     :: (fd: s32, backlog: s32) -> s32 #foreign libc;
+accept     :: (fd: s32, addr: *SockAddr, addrlen: *u32) -> s32 #foreign libc;
+read       :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;
+write      :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;
+close      :: (fd: s32) -> s32 #foreign libc;
+
+// Constants (macOS)
+AF_INET      :s32: 2;
+SOCK_STREAM  :s32: 1;
+SOL_SOCKET   :s32: 0xFFFF;
+SO_REUSEADDR :s32: 0x4;
+
+// macOS sockaddr_in (16 bytes, has sin_len field)
+SockAddr :: struct {
+    sin_len:    u8;
+    sin_family: u8;
+    sin_port:   u16;
+    sin_addr:   u32 = 0;
+    sin_zero:   u64 = 0;
+}
+
+htons :: (port: s64) -> u16 {
+    cast(u16) (((port & 0xFF) << 8) | ((port >> 8) & 0xFF))
+}