fix(docker): multi-stage build and publish tags

- Split Dockerfile into builder and runtime stages
- Put .venv on PATH so pymodbus resolves in the container
- Push image to Docker Hub and GHCR with latest and 7-char SHA tags
- Use real repo/image names in README

README.md

@@ -15,7 +15,7 @@ A configurable Modbus slave simulator for testing Modbus TCP, RTU, and TLS conne
 ### From Source
 
 ```bash
-git clone <repository-url>
+git clone https://github.com/zihluwang/modbus-slave
 cd modbus-slave
 pip install -r requirements.txt
 ```
@@ -23,7 +23,7 @@ pip install -r requirements.txt
 ### With Docker
 
 ```bash
-docker pull <username>/modbus-slave
+docker pull zihluwang/modbus-slave
 ```
 
 ## Usage
@@ -51,10 +51,10 @@ python main.py --holding-registers-default 100 --coils-default true
 
 ```bash
 # Run with defaults
-docker run -p 5020:5020 <username>/modbus-slave
+docker run -p 5020:5020 zihluwang/modbus-slave
 
 # Run with custom arguments
-docker run -p 5020:5020 <username>/modbus-slave --holding-registers-size 1000
+docker run -p 5020:5020 zihluwang/modbus-slave --holding-registers-size 1000
 ```
 
 ## Command Line Options