include/starkernel/session.h: vm_id (VMUuid), pinned (int, authoritative
over Stadium's STADIUM_FLAG_PIN per H.10), parent (VMUuid), name (fixed
64-byte buffer), identity (embedded VMIdentity, reusing the existing
type rather than inventing a new one). No logic yet, no callers -- next
step wires the session-slot array and register/find functions.
Verified 3-arch boot to ok> (amd64/aarch64/riscv64).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
