fix(ci): reduce test max_memory to 2GB for self-hosted runner

Stub tests don't need real memory. The self-hosted runner only has
2GB available, causing Nextflow to reject the 4GB process_medium cap.

Author: GeiserX

conf/test.config

@@ -18,7 +18,7 @@ params {
 
     // Limit resources for CI
     max_cpus   = 2
-    max_memory = '4.GB'
+    max_memory = '2.GB'
     max_time   = '1.h'
 
     // Stub inputs — validates pipeline wiring without real genomic data.