feat: Adds minimal cli executable and commands.

Sources/CLI/Commands/Size.swift

@@ -0,0 +1,35 @@
+import ArgumentParser
+import Dependencies
+import ManualDClient
+
+struct SizeCommand: AsyncParsableCommand {
+  static let configuration = CommandConfiguration(
+    commandName: "size",
+    abstract: "Calculate the required size of a duct."
+  )
+
+  @Option(
+    name: .shortAndLong,
+    help: "The design friction rate."
+  )
+  var frictionRate: Double = 0.06
+
+  @Argument(
+    help: "The required CFM for the duct."
+  )
+  var cfm: Int
+
+  func run() async throws {
+    @Dependency(\.manualD) var manualD
+
+    let size = try await manualD.ductSize(cfm: cfm, frictionRate: frictionRate)
+    print(
+      """
+      Calculated: \(size.calculatedSize.string(digits: 2))
+      Final Size: \(size.finalSize)
+      Flex Size: \(size.flexSize)
+      """
+    )
+
+  }
+}