Rename GUI labels to L1 Lambda / L2 Lambda, wire up L1 control

Visible captions "Lambda" and "Weight decay" renamed to "L1 Lambda" and
"L2 Lambda" in both the main params panel (MainComponent.cpp) and the
per-layer view (RbmComponent.cpp), matching the backend Rbm::Params
field names (l1Lambda, l2Lambda).

lambdaLabel's change handler was a dead stub (tooltip said "Unused",
body did nothing) -- wired it up to write params().l1Lambda, mirroring
weightDecayLabel's existing l2Lambda handler. Also added the matching
lambdaLabel->setText(...) sync in updateControls(), which weightDecay
already had but lambdaLabel never did, so the field now actually
displays the loaded value instead of always showing its default.

Verified by launching the GUI and screenshotting it: both labels render
correctly, values populate, no layout/truncation issues.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016K8Gu7Qejd11JbdiHZqYAs

source/RbmComponent.cpp

@@ -105,7 +105,7 @@ void RbmComponent::paint (Graphics& g)
 
 	g.setColour (Colours::black);
 	g.setFont (Font (15.00f, Font::plain));
-	g.drawText (TRANS("Lambda"),
+	g.drawText (TRANS("L1 Lambda"),
 				120, 306, 80, 14,
 				Justification::centred, true);
 
@@ -135,7 +135,7 @@ void RbmComponent::paint (Graphics& g)
 
 	g.setColour (Colours::black);
 	g.setFont (Font (15.00f, Font::plain));
-	g.drawText (TRANS("Weight decay"),
+	g.drawText (TRANS("L2 Lambda"),
 				296, 354, 96, 14,
 				Justification::centred, true);