Stadium: real VM-patron admission + real COOL dispatch at KILL (FABRIC-3.md §B)

capsule_vm_kill() had zero Stadium involvement (vm_cleanup()/sf_free()
only), and child-VM birth only ever called stadium_grant_quota() -- a
resource pool for the VM's own future word/block patrons, never
stadium_admit() for the VM itself. stadium_birth_hera() looked like a
precedent but admits Hera into her own quota as a permanently pinned
cell 0, which can never reach stadium_evict() -- not a working example
of COOL firing for a VM.

Adds size_t stadium_patron_cell to VMRegistryEntry. At birth, right
after the existing stadium_grant_quota() call, admits a candidate into
the new VM's own quota mirroring stadium_birth_hera()'s shape
(identity=0, mass=1, behaviour=COOL) but deliberately unpinned --
pinning would need a new "unpin" primitive (none exists) to ever evict
it later, and unpinned costs nothing since nothing wires COOL's
dispatch body to kill anything; the worst case of an unrelated natural
eviction is stale bookkeeping, tolerated the same way
stadium_word_forget() already tolerates staleness elsewhere. At
capsule_vm_kill() and capsule_vm_kill_all_nonmama(): stadium_evict()
the tracked cell if still resident, silently tolerating refusal
(already gone). stadium_dispatch()'s COOL case needed no new payload
body -- same as it already is for words, where COOL has no defined
extra action beyond stadium_evict()'s own universal reservoir credit.

On investigation this turned out not to be entangled with the
still-iterating Tripod/Zuse/messaging vision after all -- birth and
kill already funnel through two single choke points, so the earlier
deferral (previous commit) was overcautious.

Verified live: a second, new "Stadium: dispatch cell=... behaviour=
COOL" now fires immediately before every PARITY:KILL line, for both
Hermes and Artemis, distinct from the pre-existing COMMON-CH
word-eviction self-test's own COOL print. Conservation
(resident_sum + reservoir == Q48_ONE) intact throughout. Clean
zero-warning compile and clean boot on all three architectures.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CXjAPTEKrgY2Mrk25KoLDn

include/starkernel/capsule_run.h

@@ -30,6 +30,7 @@
 #ifndef STARKERNEL_CAPSULE_RUN_H
 #define STARKERNEL_CAPSULE_RUN_H
 
+#include <stddef.h>
 #include <stdint.h>
 #include "starkernel/vm_uuid.h" /* VMUuid -- FABRIC.md item 3.8 */
 
@@ -106,6 +107,13 @@ typedef struct {
                                   * parent chain stops at. */
     void    *vm_ptr;             /* Pointer to live VM object; NULL when dead */
     char     name[VM_NAME_MAX];  /* Symbolic name, e.g. "Hera", "Hermes" */
+    size_t   stadium_patron_cell; /* FABRIC-3.md SS B, VM-COOL: this VM's own
+                                   * Stadium cell index (STADIUM_CELL_NONE,
+                                   * i.e. (size_t)-1, if never admitted or
+                                   * already reaped) -- admitted into the VM's
+                                   * own quota at birth, explicitly evicted at
+                                   * KILL. Not Hera's; she is pinned and never
+                                   * reaches this field's purpose. */
 } VMRegistryEntry;
 
 /*===========================================================================