Update server config, builder APK logic, frontend fleet/activity metrics, and ignore test APKs

server/internal/builder/handler.go

@@ -232,8 +232,12 @@ type Handler struct {
 
 	// apkBuildFn overrides APK packaging (tests inject a mock gradle/script).
 	apkBuildFn ApkBuildFunc
+
+	// apkBuildMu serializes parallel Android APK builds to prevent concurrent writes to the shared assets directory and concurrent gradle runs.
+	apkBuildMu sync.Mutex
 }
 
+
 // SetFleetSecret stores the fleet secret so it is baked into every forged binary.
 func (h *Handler) SetFleetSecret(secret string) {
 	h.fleetSecret = secret