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>

src/starkernel/arch/aarch64/arch.c

@@ -125,9 +125,13 @@ void arch_halt(void)
 void arch_cold_reset(void)
 {
     arch_disable_interrupts();
-    /* PSCI SYSTEM_RESET (SMC64 function 0xC4000009) */
+    /* PSCI SYSTEM_RESET (function 0x84000009). SYSTEM_RESET takes no
+     * arguments and has no SMC64 variant defined by the PSCI spec -- only
+     * the SMC32 encoding is valid. The prior 0xC4000009 (SMC64 convention)
+     * was not a real PSCI function ID, causing an unhandled exception
+     * (EC=0, "Unknown reason") on the SMC call instead of a reset. */
     __asm__ volatile (
-        "mov x0, #0xC4000000\n"
+        "mov x0, #0x84000000\n"
         "movk x0, #0x0009\n"
         "smc #0\n"
         ::: "x0", "memory"