diagnostic(arm64): F13 GIC audit and idle-scan breadcrumbs

[ryanbreen]

Summary

• extend ARM64 GIC CPU audit capture for SRE/CTLR/PMR/IGRPEN1/MPIDR
• dump target GICR state at SPI34 timeout for recent SGI target CPUs
• add idle-scan AHCI ring breadcrumbs around isr_unblock_for_io target selection
• append F13 investigation findings and F14 recommendation

Validation

• cargo build --release --target aarch64-breenix.json -Z build-std=core,alloc -Z build-std-features=compiler-builtins-mem -p kernel --bin kernel-aarch64
• 5x ./run.sh --parallels --test 60 under logs/breenix-parallels-cpu0/f13-gic-audit/run{1..5}/

Result

• build clean, zero warnings/errors
• sweep still FAIL: 2/5 no AHCI timeout, 3/5 AHCI timeout
• all 5 runs captured 8 GIC_CPU_AUDIT rows
• failing runs captured GICR_STATE; run4 captured last scan verdict UNBLOCK_SCAN_CPU / UNBLOCK_PER_SGI