feat: Adds psi to feet of head conversion.

Sources/ViewController/HomePage.swift

@@ -67,6 +67,12 @@ struct HomePage: HTML, Sendable {
         svg: .circleGauge,
         route: .hydronicSystemPressure(.index)
       )
+      group(
+        label: "Feet of Head",
+        description: FeetOfHead.description,
+        svg: .footprints,
+        route: .feetOfHead(.index)
+      )
     }
   }