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.

examples/1025-errors-trace-format.sx

@@ -1,4 +1,4 @@
-// Error return-trace formatting (ERR step E3.3). `library/modules/trace.sx`
+// Error return-trace formatting (ERR step E3.3). `library/modules/std/trace.sx`
 // reads the trace buffer (E3.1, populated by E3.2's raise/try push wiring) and
 // renders it. `trace.print_current()` writes the trace to stderr; the catch
 // handler sees the full chain because the absorption clear fires at handler
@@ -9,7 +9,7 @@
 // snapshot shows the trace lines interleaved with the `print` (stdout) lines.
 
 #import "modules/std.sx";
-trace :: #import "modules/trace.sx";
+trace :: #import "modules/std/trace.sx";
 
 // Buffer length probe (the runtime symbol; public read API is the trace module).
 sx_trace_len :: () -> u32 #foreign;