feat(audit): 1.3 — CPU collector (dmidecode type 4, microcode)

- cpu.go: collectCPUs(), parseCPUs(), parseCPUSection()
- splitDMISections(): splits multi-section dmidecode output generically
- parseFieldLines(): reusable key→value parser for DMI sections
- parseCPUStatus(): Populated/Unpopulated → OK/WARNING/EMPTY/UNKNOWN
- parseSocketIndex(): CPU0/Processor 1/Socket 2 → integer
- cleanManufacturer(): strips (R), Corporation, Inc. suffixes
- parseMHz(), parseInt(): field value parsers
- Serial fallback: <board_serial>-CPU-<socket> when DMI serial absent
- readMicrocode(): /sys/devices/system/cpu/cpu0/microcode/version
- cpu_test.go: dual-socket, unpopulated skipped, status, socket, manufacturer, MHz

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/collector/collector.go

@@ -21,7 +21,11 @@ func Run() schema.HardwareIngestRequest {
 	snap.Board = board
 	snap.Firmware = append(snap.Firmware, biosFW...)
 
-	// remaining collectors added in steps 1.3 – 1.10
+	cpus, cpuFW := collectCPUs(snap.Board.SerialNumber)
+	snap.CPUs = cpus
+	snap.Firmware = append(snap.Firmware, cpuFW...)
+
+	// remaining collectors added in steps 1.4 – 1.10
 
 	slog.Info("audit completed", "duration", time.Since(start).Round(time.Millisecond))