Zuse default-attach: xHCI initial-port-scan fix, ZUSEDISK wiring, mismatched-marker resync

xhci_bringup() now scans for already-connected ports at bring-up
(xhci_scan_ports_for_already_connected()), not just later hotplug events,
so a USB device present on the QEMU command line at launch is detected.
Makefile.starkernel attaches disk/zuse.img on the xhci0 bus by default in
all three arch qemu targets (ZUSEDISK=, empties for a bare boot).

capsule_mint_identity() gained a drive_known_blank param to skip a fully
redundant second homeblocks_sig_check() when the caller already confirmed
HOMEBLOCKS_SIG_BLANK itself.

Root-caused what looked like a hang after the drive attached: Artemis's
fence still carried a genesis marker from before a mid-session reformat,
while the reformatted disk/zuse.img read back BLANK -- a mismatched pair
capsule_zuse_boot_try_attach() correctly declined to act on, leaving the
boot idling at a plain ok> with nothing left to log (indistinguishable
from a hang under slow TCG). Fixed by zeroing both disk/artemis.img and
disk/zuse.img at their original sizes, giving a matched blank pair.
Verified full three-architecture acceptance: amd64 fresh genesis-mint,
aarch64/riscv64 clean reload against the same now-minted images.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KBjfeLPo71sUQ8zC7V7P5m

capsules/BLOCK_MAP.md

@@ -1,5 +1,5 @@
 # Capsule Block Manifest — Auto-generated
-<!-- Generated by mkcapsule --manifest  2026-08-28T22:27:23Z -->
+<!-- Generated by mkcapsule --manifest  2026-08-29T01:39:10Z -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
 <!-- in MANIFEST.md alongside this auto-generated index.      -->