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

go.mod

@@ -0,0 +1,10 @@
+module github.com/warkanum/unitdore
+
+go 1.26.1
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/cobra v1.10.2 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)