feat: Adds psi to feet of head conversion.

Sources/ViewController/Views/FeetOfHead.swift

@@ -0,0 +1,70 @@
+import Elementary
+import ElementaryHTMX
+import PsychrometricClient
+import Routes
+import Styleguide
+
+struct FeetOfHeadForm: HTML, Sendable {
+  let response: FeetOfHead.Response?
+
+  typealias Key = FeetOfHead.Request.FieldKey
+
+  var content: some HTML {
+    FormHeader(label: "Feet of Head", svg: .footprints)
+
+    form(
+      .hx.post(route: .feetOfHead(.index)),
+      .hx.target("#result")
+    ) {
+      div(.class("space-y-6")) {
+        div(.class("grid grid-cols-2 gap-4")) {
+          LabeledContent(label: "Pressure (psi)") {
+            Input(id: Key.pressure, placeholder: "Pressure")
+              .attributes(.type(.number), .min("0.1"), .step("0.1"), .autofocus, .required)
+          }
+
+          LabeledContent(label: "Water Temperature (\(String.fahrenheit))") {
+            Input(id: Key.waterTemperature, placeholder: "Temperature (optional)")
+              .attributes(.type(.number), .min("32.0"), .step("0.1"))
+          }
+        }
+
+        Note {
+          """
+          If water temperature is not supplied, then calculations will be based on 60\(String.fahrenheit) water.
+          """
+        }
+
+        div {
+          SubmitButton(label: "Feet of Head")
+        }
+      }
+    }
+
+    div(.id("result")) {
+      if let response {
+        FeetOfHeadResponse(response: response)
+      }
+    }
+  }
+}
+
+struct FeetOfHeadResponse: HTML, Sendable {
+  let response: FeetOfHead.Response
+
+  var content: some HTML {
+    ResultContainer(reset: .feetOfHead(.index)) {
+      ResultBox {
+        div(.class("grid grid-cols-2")) {
+          VerticalGroup(label: "Feet of Head", value: "\(double: response.feetOfHead)", valueLabel: "ft.")
+          VerticalGroup(
+            label: "Water Density",
+            value: "\(double: response.density.value)",
+            valueLabel: response.density.units.rawValue
+          )
+        }
+      }
+      WarningBox(warnings: response.warnings)
+    }
+  }
+}