feat: Begins hvac system performance

Sources/ViewController/Views/MainPage.swift

@@ -77,6 +77,14 @@ private struct Header: HTML {
               "Dehumidifier-Sizing"
             }
           }
+          li {
+            a(
+              .class("hover:border-b \(border: .yellow)"),
+              .hx.get(route: .hvacSystemPerformance(.index)), .hx.target("#content"), .hx.pushURL(true)
+            ) {
+              "HVAC-System-Performance"
+            }
+          }
         }
       }
     }
@@ -88,7 +96,7 @@ private struct PageContent<Body: HTML>: HTML where Body: Sendable {
 
   var content: some HTML {
     div(.class("mx-5 lg:mx-20")) {
-      div(.class("rounded-xl shadow-lg bg-white dark:bg-slate-700 p-8")) {
+      div(.class("rounded-xl shadow-lg bg-white dark:bg-slate-700 p-8 text-gray-600 dark:text-slate-200")) {
         div(.id("content")) {
           body()
         }