Migrate Hera->Artemis storage-attach to a real message round-trip

Hera still polls xHCI and sig-checks attached drives, but the storage
registration step (blk_subsys_attach_device(), now wrapped as the
BLK-ATTACH primitive) moves to Artemis's own dictionary, reached via
HERA-BLK-ATTACH-REQ/BLK-ATTACH-ACK (VM-EXEC, since Hera can't load her
own messaging.4th -- see the doc comment in repl.c). Identity birth
(Zuse genesis / WIREBIND) is deferred until the ack confirms storage
actually succeeded, instead of running synchronously underneath a
storage call that might fail ("wait for ack, safer for identity data").

Caught and fixed a real bug live during acceptance testing: Artemis's
ACK-APPEND-NUM fed a single-cell value into <# #S #> (which expects a
double-cell pair), causing a stack underflow the first time
HERA-BLK-ATTACH-REQ ran. Fixed with the same `0 SWAP` convention every
other numeric-append helper in this codebase already uses.

Verified booting clean to (zuse) ok> with no VM-EXEC errors on all
three architectures (amd64/aarch64/riscv64).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014Ec88YKxxhZGG1RNnune78

logs/20260907-120949/aarch64/qemu-aarch64-20260907-120949.log

@@ -0,0 +1,2 @@
+UEFI firmware (version 2025.11-3ubuntu7 built at 11:11:58 on Mar 31 2026)
+[=3h