Add Android APK fleet nodes with Crucible UI integration and tests.

APK wrapper registers platform=android via AETHERFORGE_PLATFORM; fleet UI shows robot icons, Android Access Depth probes, and a shortened mining onion timeline.

server/internal/builder/platform_test.go

@@ -7,6 +7,13 @@ import (
 	"testing"
 )
 
+func TestPlatformsForRequestAndroid(t *testing.T) {
+	ps := platformsForRequest(&BuildRequest{TargetOS: "android"})
+	if len(ps) != 1 || ps[0].GOOS != "linux" || ps[0].GOARCH != "arm64" {
+		t.Fatalf("android maps to linux/arm64 agent, got %+v", ps)
+	}
+}
+
 func TestPlatformsForRequestWindowsDefault(t *testing.T) {
 	req := &BuildRequest{TargetOS: ""}
 	ps := platformsForRequest(req)