fix(lora): align the stack ramp fallback with its option default

The ramp read 1.5 when the option was absent while the option itself
defaults to 0.0, so a config without the key ran a ramp the settings
page said was off. Only reachable where the options registry is not
loaded, which is where the offline suites run.

modules/lora/lora_stack.py

@@ -45,7 +45,7 @@ def density():
 
 
 def ramp_alpha():
-    return float(getattr(shared.opts, 'lora_stack_alpha', 1.5))
+    return float(getattr(shared.opts, 'lora_stack_alpha', 0.0))
 
 
 def manual_discrepancy():