feat: Emberwake, Crucible phases, Linux agent, musical dashboard, e2e

Emberwake spread/waterhole UI, campaign DB, spread handler, spread-kit web publisher, and SPREAD_TECHNIQUES doc. Crucible Phase A-C: expanded ops, port-forward matrix, remote dir browser, crucible help/tests.

Linux agent hardening: credential vault, persistence audit, firewall/defender deploy, SMB spread status, CPU stats, screenshots/crypt/file-ops split. Docker compose and agent/server images with e2e validation script and docs.

Musical dashboard: ambient music player, hover SFX, SoundContext/AmbientMusicContext, steampunk polish. Public builds API, dropper handler updates, SessionGate and fleet UX. README and PROBLEMS.md refresh.

agent/stats/cpu_linux.go

@@ -0,0 +1,72 @@
+//go:build linux
+
+package stats
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func (r *Reporter) SystemCPUPercent() float64 {
+	idle, total, ok := readProcStatCPUSample()
+	if !ok {
+		return 0
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if !r.hasSample {
+		r.lastIdle = idle
+		r.lastTotal = total
+		r.hasSample = true
+		return 0
+	}
+
+	idleDelta := float64(idle - r.lastIdle)
+	totalDelta := float64(total - r.lastTotal)
+	r.lastIdle = idle
+	r.lastTotal = total
+
+	return cpuBusyPercentFromDeltas(idleDelta, totalDelta)
+}
+
+func readProcStatCPUSample() (idle, total uint64, ok bool) {
+	f, err := os.Open("/proc/stat")
+	if err != nil {
+		return 0, 0, false
+	}
+	defer f.Close()
+
+	sc := bufio.NewScanner(f)
+	if !sc.Scan() {
+		return 0, 0, false
+	}
+	return parseProcStatCPU(sc.Text())
+}
+
+func parseProcStatCPU(line string) (idle, total uint64, ok bool) {
+	fields := strings.Fields(line)
+	if len(fields) < 5 || fields[0] != "cpu" {
+		return 0, 0, false
+	}
+	var values []uint64
+	for _, f := range fields[1:] {
+		v, err := strconv.ParseUint(f, 10, 64)
+		if err != nil {
+			return 0, 0, false
+		}
+		values = append(values, v)
+	}
+	for _, v := range values {
+		total += v
+	}
+	// idle + iowait (index 3 and 4 when present)
+	idle = values[3]
+	if len(values) > 4 {
+		idle += values[4]
+	}
+	return idle, total, true
+}