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

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