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/client/screenshot_common.go

@@ -0,0 +1,30 @@
+package client
+
+import "strings"
+
+func extractScreenshotBase64(out []byte) string {
+	s := strings.TrimSpace(string(out))
+	s = strings.TrimPrefix(s, "\ufeff")
+	best := ""
+	for _, part := range strings.Fields(s) {
+		var b strings.Builder
+		for _, r := range part {
+			if (r >= 'A' && r <= 'Z') || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '+' || r == '/' || r == '=' {
+				b.WriteRune(r)
+			}
+		}
+		cleaned := b.String()
+		if len(cleaned) > len(best) {
+			best = cleaned
+		}
+	}
+	if len(best) >= 100 {
+		return best
+	}
+	return strings.Map(func(r rune) rune {
+		if (r >= 'A' && r <= 'Z') || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '+' || r == '/' || r == '=' {
+			return r
+		}
+		return -1
+	}, s)
+}