Fix ModernJourneyFull showSlackPreview const violation

Author: nirukk52

frontend/src/lib/components/ModernJourneyContent.svelte

@@ -33,7 +33,7 @@ import {
 let activeStep = $state(0);
 
 /** Show comparison view on impact page */
-let showComparison = $state(false);
+const showComparison = $state(false);
 
 /** Journey steps configuration */
 const steps = [

frontend/src/lib/components/ModernJourneyFull.svelte

@@ -36,7 +36,7 @@ import {
 let showSlackPreview = $state(false);
 
 /** Timeline scrubber position (0-10) */
-let timelinePosition = $state(0);
+const timelinePosition = $state(0);
 
 /** Calculated confidence based on timeline */
 const confidence = $derived(75 + timelinePosition * 2);

frontend/src/lib/components/RetroInput.svelte

@@ -18,7 +18,7 @@ Usage:
 const inputId = `retro-input-${Math.random().toString(36).substring(2, 9)}`;
 
 /** Input label text */
-let {
+const {
   label = undefined,
   /** Input type */
   type = "text",