feat: add UMS CLI for binary packaging and system initialization

- Add Cobra-based CLI with ums init, ums serve, ums version commands
- ums init supports interactive prompts and non-interactive flags
- Generates secure JWT secrets and config.yaml automatically
- Extract server.Serve() function for reuse
- Add cross-platform build targets to Makefile
- Update README with CLI installation and usage instructions

New files:
- cmd/ums/main.go - CLI entry point
- cmd/ums/cmd/root.go - Root command
- cmd/ums/cmd/init.go - Interactive/non-interactive init
- cmd/ums/cmd/serve.go - Server command
- cmd/ums/cmd/version.go - Version command
- internal/server/server.go - Extracted Serve function

go.mod

@@ -60,6 +60,7 @@ require (
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/icholy/digest v1.1.0 // indirect
 	github.com/imroc/req/v3 v3.57.0 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
@@ -89,7 +90,8 @@ require (
 	github.com/sourcegraph/conc v0.3.0 // indirect
 	github.com/spf13/afero v1.11.0 // indirect
 	github.com/spf13/cast v1.6.0 // indirect
-	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/spf13/cobra v1.9.1 // indirect
+	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
 	github.com/tencentcloud/tencentcloud-sdk-go/tencentcloud/common v1.3.57 // indirect
 	github.com/tencentcloud/tencentcloud-sdk-go/tencentcloud/sms v1.3.57 // indirect
@@ -110,6 +112,7 @@ require (
 	golang.org/x/net v0.52.0 // indirect
 	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/term v0.41.0 // indirect
 	golang.org/x/text v0.35.0 // indirect
 	golang.org/x/tools v0.43.0 // indirect
 	google.golang.org/appengine v1.6.8 // indirect