Make Start button bigger and position at the bottom of check-in card

Fixes #15

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PortfolioJournal/Views/Dashboard/DashboardView.swift

@@ -483,11 +483,6 @@ struct MonthlyCheckInCard: View {
                     }
                     .font(.subheadline.weight(.semibold))
                 }
-
-                Button("Start") {
-                    showingStartOptions = true
-                }
-                .font(.subheadline.weight(.semibold))
             }
 
             ProgressView(value: checkInProgress)
@@ -499,6 +494,18 @@ struct MonthlyCheckInCard: View {
                     .foregroundColor(isOverdue ? .red : .secondary)
             }
 
+            Button {
+                showingStartOptions = true
+            } label: {
+                Text("Start")
+                    .font(.headline.weight(.semibold))
+                    .frame(maxWidth: .infinity)
+                    .padding(.vertical, 12)
+                    .background(Color.appPrimary)
+                    .foregroundColor(.white)
+                    .cornerRadius(AppConstants.UI.cornerRadius)
+            }
+
             NavigationLink(
                 isActive: $startDestinationActive
             ) {