feat(layout): relax MAM_MIN_PANE_COLS to 15 and remove vertical height constraints for scrollable terminal split

.mam.env.example

@@ -128,13 +128,14 @@
 #default: 3
 # SKS_EMPTY_GIVEUP=3
 
-# Minimum columns a pane must retain after a vertical split (2xK layout engine).
-#default: 40
-# MAM_MIN_PANE_COLS=40
+# Minimum columns a pane must retain after a horizontal/column split (2xK layout engine).
+#default: 15
+# MAM_MIN_PANE_COLS=15
 
-# Minimum rows a pane must retain after a horizontal split (2xK layout engine).
-#default: 20
-# MAM_MIN_PANE_ROWS=20
+# Minimum rows a pane must retain after a vertical split (2xK layout engine).
+# Set to 0 to disable vertical row constraints (terminal scrollback handles height).
+#default: 0
+# MAM_MIN_PANE_ROWS=0
 
 # Maximum number of columns a workspace may grow to before the engine reports
 # 'overflow' (which makes lib.sh create a fresh workspace instead of splitting).