feat(01-01): generate and build hello app from manifest

- Add summer build with validated summer.yaml codegen
- Generate stable main.go and plugins.gen.go then go build
- Smoke-test the built hello binary greeter:hello command

cmd/summer/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"git.golem15.com/golem15/summercms/bonfire"
+	"git.golem15.com/golem15/summercms/internal/build"
+)
+
+func main() {
+	root := bonfire.NewRoot("summer", []bonfire.Command{buildCommand()}, os.Stdout)
+	root.SetArgs(os.Args[1:])
+	if err := root.Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func buildCommand() bonfire.Command {
+	return bonfire.Command{
+		Name:        "build",
+		Description: "Generate plugin imports and build the app binary",
+		Run: func(ctx context.Context, in bonfire.Input, out bonfire.Output) error {
+			dir, err := os.Getwd()
+			if err != nil {
+				return err
+			}
+			return build.App(ctx, dir, out)
+		},
+	}
+}