arena (25.3b): LOCAL sites allocate from the frame's scratch; dispatch is not an allocation; @frame by property

Behind ludicc --arena (or 'arena on' in the program's package.ludic): the escape analysis runs and a
LOCAL site's allocation raises @lp_want for that one call, so it comes from the frame's arena. Two
halves in one mmap reservation (R3D_ARENA_MB each, 256 by default), bump-allocated with a 16-byte
size header, flipped at each frame mark: a frame's scratch is good through the next frame, then its
half is started again (R3D_ARENA_CHECK=1 fills it with 0xDD first). The heap takes over when no frame
is running, off the main thread, or past the half's end; lp_free ignores an arena block and
lp_realloc copies one out. R3D_ARENA=0 turns it off at run time; the census reports each half's
high-water mark. A program that builds text, a list and a record per frame: 29998 heap blocks made
and 18002 freed without it, 8 and 8 with it and 544 bytes of scratch a frame, the same output.

A dispatch's 'new' fills the queue's kept record (E_NEW.b), so 25.2 no longer counts it and 25.3
treats its fields as kept. '@frame' is keyed by property and field: a 'run' field is a root only in
a property that marks it, and 'tick' stays a System's.

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

selfhost/backend/stdlib/emit_pak.ludic

@@ -94,7 +94,7 @@ function emit_pak_prelude() -> void {
     emith("declare i32 @open(ptr, i32, ...)\n")
     emith("declare i32 @close(i32)\n")
     emith("declare i64 @lseek(i32, i64, i32)\n")
-    emith("declare ptr @mmap(ptr, i64, i32, i32, i32, i64)\n")
+    if not g_mmap_declared { emith("declare ptr @mmap(ptr, i64, i32, i32, i32, i64)\n");  g_mmap_declared = true }
     emith("declare ptr @fmemopen(ptr, i64, ptr)\n")
     emith("declare i32 @chdir(ptr)\n")
     emith("declare i32 @_NSGetExecutablePath(ptr, ptr)\n")