Initial commit: unitdore scaffold + syncup/edit commands

- config: load/save/add unit, Unit struct
- runtime: podman + docker discovery and exists check
- cmd: syncup (discover + reconcile), edit, cobra root
- PLAN.md: full project plan

main.go

@@ -0,0 +1,7 @@
+package main
+
+import "github.com/warkanum/unitdore/cmd"
+
+func main() {
+	cmd.Execute()
+}