item 4.6: fix Stadium quota-grant ordering; fix aarch64 PSCI SYSTEM_RESET function ID

Artemis's 30-rep surface stress campaign was failing 100% of trials on all
three architectures: stadium_grant_quota() ran after IDENTITY exec in
capsule_birth.c, but Artemis's init.4th auto-runs the stress campaign as
part of that same IDENTITY exec, so every STADIUM-ADMIT call during it hit
a nonexistent quota slot and refused unconditionally. Moved the grant call
before IDENTITY exec. Verified 30/30 reps PASS on amd64, aarch64, and
riscv64 post-fix (was 30/30 FAIL on all three pre-fix).

Also fixed an independent, real bug found during the same acceptance pass:
aarch64's arch_cold_reset() issued PSCI SYSTEM_RESET using the SMC64
calling convention (0xC4000009), which is not a valid PSCI function ID --
SYSTEM_RESET has no SMC64 variant. Corrected to the SMC32 encoding
(0x84000009). This did not resolve the separate aarch64 BYE cold-restart
exception also found in this pass (root cause not yet found, tested and
refuted an interrupt-race hypothesis, documented in FABRIC-2.md Section I
for follow-up) but is a genuine spec fix worth keeping regardless.

Full writeup, evidence, and the still-open aarch64 crash investigation in
FABRIC-2.md Sections H and I.

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

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