Phase 8: zuse cert storage moved out of the dictionary (fuse-blow install)

Found that a pinned CONSTANT is not actually tamper-proof: ACL-PIN only
blocks redefinition, not a >BODY-then-store on the word's existing data
field. Moves the Zuse cert value into C-only VM struct fields
(zuse_cert_lo/hi + zuse_cert_installed fuse bit) with a one-time
vm_zuse_cert_install() and read-only ZUSE-CERT-LO@/HI@/INSTALLED? FORTH
accessors, closing the tamper path structurally instead of by convention.
Deletes the now-insecure ZUSE-CERT-LO/HI CONSTANT words from zuse.4th.

vm_zuse_cert_install() has no caller yet -- the real mint flow (Milestone
6 CA, the MINT word) is still open; this is storage + accessors only, not
a stand-in mint. Documented in FABRIC-3.md. Verified: hosted build clean,
mkcapsule --lint clean (31/31), clean boot to ok> on amd64/aarch64/riscv64
with Stadium conservation intact and no panics.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U14ET9CWAtbQMbYqomKgXd

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