feat: project init with config package and root command

Go module, cobra root command, config resolution (CTASK_ROOT, CTASK_AGENT, EnvVars) with tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/root.go

@@ -0,0 +1,24 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var version = "0.1.0"
+
+var rootCmd = &cobra.Command{
+	Use:   "ctask",
+	Short: "Create and manage AI-agent task workspaces",
+	Long:  "ctask is a local CLI that creates and manages named AI-agent task workspaces so developers can start, resume, and organize work more safely and predictably.",
+}
+
+func Execute() error {
+	return rootCmd.Execute()
+}
+
+func init() {
+	rootCmd.Version = version
+	rootCmd.SetVersionTemplate(fmt.Sprintf("ctask v%s\n", version))
+}