Implemented phase 2 for the POC prototype in the Website service.

Services/Website/Sources/Library/Internal/Components/Unavailable.swift

@@ -0,0 +1,41 @@
+import Elementary
+
+/// An action the prototype shows but does not build: a button that is visibly, and audibly, unavailable.
+struct Unavailable: HTML {
+
+    // MARK: Properties
+
+    /// The action's name.
+    let label: String
+
+    /// A modifier class sizing or styling the button, or `nil` for none.
+    let modifier: String?
+
+    // MARK: Initializers
+
+    /// Creates an unavailable action.
+    /// - Parameters:
+    ///   - label: the action's name.
+    ///   - modifier: a modifier class sizing or styling the button, or `nil` (the default) for none.
+    init(
+        _ label: String,
+        modifier: String? = nil
+    ) {
+        self.label = label
+        self.modifier = modifier
+    }
+
+    // MARK: Computed
+
+    var body: some HTML {
+        button(
+            .class(["button", modifier].compactMap(\.self).joined(separator: " ")),
+            .type(.button),
+            .disabled,
+            .title("Not part of the prototype")
+        ) {
+            label
+        }
+    }
+
+}