starkernel: item 3.8 -- VM identifiers as UUID/GUID

Punch list §25 item 3.8 complete. Added after starting item 4.1
surfaced the need to thread a vm_id into stadium_admit()'s new quota
parameter; Captain Bob ruled UUID/GUID rather than keeping the
narrower uint32_t.

New VMUuid type (vm_uuid.h/vm_uuid.c): two uint64_t halves, RFC-4122-
shaped for logging. Not real randomness -- checked directly against
QEMU 10.2.1's actual CPU feature set: amd64 RDRAND and riscv64 Zkr are
both real, available features here; aarch64 has no RNG property on any
CPU model including "max" (verified exhaustively via QMP
query-cpu-model-expansion). Captain Bob ruled a uniform fallback
across all three ISAs rather than a per-architecture split.

Fallback is a deterministic PRNG (splitmix64) seeded from the Mama
capsule's content hash, pre-filling a 16-entry FIFO pool at boot and
refilling with another batch of the same stream when exhausted --
exactly the shape requested. Same capsule booted twice produces the
same id sequence, preserving the dict_hash reproducibility this
session has relied on throughout.

Hera keeps a fixed, reserved all-zero id, not drawn from the pool --
capsule_birth.c uses vm_id == 0 as a load-bearing sentinel in three
places (KILL protection x2, fleet heat-fanout parent-chain
terminator), found by reading before writing any code.

Two real sentinel-collision bugs caught before shipping, same class as
STADIUM_CONTAINS_NONE: vm_uuid_none() (all-ones, not all-zero) for
"not yet assigned"/"no VM" placeholders; confirmed item 3.7's quota
table already used an in_use boolean rather than a vm_id sentinel, so
no second collision was actually possible there -- the dead,
never-referenced STADIUM_QUOTA_SLOT_EMPTY macro was removed.

Blast radius larger than first scoped, flagged mid-work rather than
silently absorbed: capsule_vm_physics.c/.h (the fleet heat-transfer
layer item 2.1 modified earlier this session) has its own vm_id-keyed
node table and walks parent_vm_id chains through the same identity
space, so it needed the same change, plus its callers in
mama_forth_words.c and sk_vm_bootstrap.c.

One live FORTH word contract changed, by explicit ruling: CAPSULE-BIRTH
was ( capsule-id -- vm-id ), a single cell -- can't hold 128 bits.
Captain Bob picked pushing two cells ("there is doubles support in the
FORTH std word set anyway"): ( capsule-id -- vm-id-hi vm-id-lo ).
MAMA-VM-ID changed the same way: ( -- 0 0 ).

Verified: full (not standalone-file) kernel rebuild to catch cross-file
breakage given the size of this change -- it surfaced the
capsule_vm_physics.c blast radius a narrower check would have missed.
Three-architecture boot (amd64, aarch64, riscv64), all reaching ok>
with identical dict_hash=0x3d4e1daf289da94f matching the item-3.7
baseline.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

include/starkernel/capsule_birth.h

@@ -137,7 +137,7 @@ CapsuleRunResult capsule_birth_baby(
     const CapsuleDesc *descs,
     const CapsuleNameEntry *names,
     const uint8_t *arena,
-    uint32_t *out_vm_id,
+    VMUuid *out_vm_id,
     void **out_vm_ctx
 );
 
@@ -216,7 +216,7 @@ int capsule_vm_kill(const char *name);
  * @param out    Output: registry entry copy
  * @return 0 on success, -1 if not found
  */
-int capsule_vm_registry_get(uint32_t vm_id, VMRegistryEntry *out);
+int capsule_vm_registry_get(VMUuid vm_id, VMRegistryEntry *out);
 
 /**
  * capsule_vm_registry_count - Get number of registered VMs
@@ -252,7 +252,7 @@ int capsule_vm_find_by_name_nocase(const char *name, VMRegistryEntry *out);
  * @param vm_id  VM ID to update
  * @param state  New VMState value
  */
-void capsule_vm_set_state(uint32_t vm_id, uint32_t state);
+void capsule_vm_set_state(VMUuid vm_id, uint32_t state);
 
 /**
  * capsule_vm_registry_set_name - Assign a symbolic name to a registered VM
@@ -262,7 +262,7 @@ void capsule_vm_set_state(uint32_t vm_id, uint32_t state);
  * @param vm_id  VM ID to name
  * @param name   Symbolic name string
  */
-void capsule_vm_registry_set_name(uint32_t vm_id, const char *name);
+void capsule_vm_registry_set_name(VMUuid vm_id, const char *name);
 
 /**
  * capsule_vm_kill_all_nonmama - Kill every non-Mama VM in the registry.