feat(goctl/rpc): support external proto imports with cross-package ty… (#5472)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tools/goctl/rpc/example/01-basic/README.md

@@ -0,0 +1,100 @@
+# Example 01: Basic RPC Service
+
+This is the simplest example of generating an RPC service with goctl.
+
+## Proto Definition
+
+A single `greeter.proto` file with one service and one RPC method, no external imports.
+
+The `go_package` uses a full module path:
+
+```protobuf
+option go_package = "example.com/demo/greeter";
+```
+
+## Generation Commands
+
+### Method 1: Quick Start with `goctl rpc new`
+
+```bash
+# Create a complete RPC project with one command
+goctl rpc new greeter
+```
+
+This generates the proto file and service code together:
+
+```
+greeter/
+├── etc
+│   └── greeter.yaml
+├── greeter
+│   ├── greeter.pb.go
+│   └── greeter_grpc.pb.go
+├── greeter.go
+├── greeter.proto
+├── greeterclient
+│   └── greeter.go
+└── internal
+    ├── config
+    │   └── config.go
+    ├── logic
+    │   └── pinglogic.go
+    ├── server
+    │   └── greeterserver.go
+    └── svc
+        └── servicecontext.go
+```
+
+### Method 2: Generate from an Existing Proto
+
+First, initialize the output directory with a `go.mod`:
+
+```bash
+mkdir -p output && cd output && go mod init example.com/demo && cd ..
+```
+
+Then generate the code:
+
+```bash
+goctl rpc protoc greeter.proto \
+  --go_out=output \
+  --go-grpc_out=output \
+  --zrpc_out=output \
+  --go_opt=module=example.com/demo \
+  --go-grpc_opt=module=example.com/demo \
+  --module=example.com/demo \
+  -I .
+```
+
+Generated directory structure:
+
+```
+output/
+├── etc
+│   └── greeter.yaml
+├── go.mod
+├── greeter
+│   ├── greeter.pb.go
+│   └── greeter_grpc.pb.go
+├── greeter.go
+├── greeterclient
+│   └── greeter.go
+└── internal
+    ├── config
+    │   └── config.go
+    ├── logic
+    │   └── sayhellologic.go
+    ├── server
+    │   └── greeterserver.go
+    └── svc
+        └── servicecontext.go
+```
+
+## Key Points
+
+- This is the simplest scenario: one proto file, one service, one RPC method.
+- The `go_package` uses a full module path (`example.com/demo/greeter`), not a relative path.
+- The `--module` flag tells goctl the Go module name; `--go_opt=module=...` and `--go-grpc_opt=module=...` tell protoc to strip the module prefix from output paths.
+- The `--zrpc_out` flag specifies where the goctl-generated service code goes.
+- The `--go_out` and `--go-grpc_out` flags specify where protoc-generated code goes.
+- Edit the logic file (`internal/logic/sayhellologic.go`) to implement your business logic.