docs: add comprehensive documentation for project setup and usage

- Add CLAUDE.md with detailed guidelines for using Claude Code in this repository
- Document project architecture, key files, and composite action behavior
- Explain automated testing strategy using Docker containers and GitHub Actions
- Provide instructions for local testing and key troubleshooting tips
- Describe supported features: script execution methods, environment variable handling, multiple host support, and error handling patterns
- Outline steps for adding new action parameters and keeping documentation up to date
- Clarify version management and the release process for the action

Signed-off-by: appleboy <appleboy.tw@gmail.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a GitHub Action for executing remote SSH commands. Built using a composite action pattern, it downloads and runs the [drone-ssh](https://github.com/appleboy/drone-ssh) binary (written in Go) to execute SSH commands on remote hosts.
+
+**Key characteristics:**
+
+- No local compilation required - downloads pre-built binaries from drone-ssh releases
+- Shell-based composite action using `entrypoint.sh`
+- Supports password and SSH key authentication, proxies, multiple hosts, and environment variable passing
+- All input parameters are passed via `INPUT_*` environment variables
+
+## Architecture
+
+### Execution Flow
+
+1. **action.yml** - GitHub Actions composite action definition
+   - Defines all input parameters and their descriptions
+   - Sets up environment variables with `INPUT_*` prefix
+   - Calls `entrypoint.sh`
+
+2. **entrypoint.sh** - Main entry point
+   - Detects platform (Linux/Darwin/Windows) and architecture (amd64/arm64)
+   - Downloads appropriate `drone-ssh` binary from GitHub releases
+   - Executes the binary with all environment variables
+   - Handles `capture_stdout` for output capture
+
+3. **drone-ssh binary** - The actual SSH client (separate Go project)
+   - Performs SSH connection and command execution
+   - Not part of this repository
+
+### Key Files
+
+- `action.yml` - Action metadata and input/output definitions
+- `entrypoint.sh` - Platform detection, binary download, and execution
+- `testdata/` - Test scripts and SSH keys for CI workflows
+- `.github/workflows/main.yml` - Comprehensive test suite using Docker containers
+
+## Testing
+
+### Running Tests
+
+Tests run automatically via GitHub Actions workflows. The test suite uses Docker containers running OpenSSH servers:
+
+```bash
+# Tests run automatically on push via .github/workflows/main.yml
+# Tests create Docker containers with openssh-server and test various scenarios
+```
+
+### Test Categories (from main.yml)
+
+The test workflow covers:
+
+- **default-user-name-password**: Basic password authentication
+- **check-ssh-key**: RSA key authentication, key priority over password
+- **support-key-passphrase**: Encrypted SSH keys
+- **multiple-server**: Multiple hosts with different ports
+- **support-ed25519-key**: ED25519 key format
+- **testing-with-env**: Environment variable passing, `allenvs`, custom formats
+- **testing06**: IPv6 connectivity
+- **testing07**: Special characters in passwords
+- **testing-capturing-output**: Output capture functionality
+- **testing-script-stop**: Script error handling with `set -e`
+- **testing-script-error**: Error propagation
+
+### Testing Locally
+
+Since this action downloads binaries, local testing should:
+
+1. Create a test SSH server (Docker or VM)
+2. Test `entrypoint.sh` directly with appropriate `INPUT_*` environment variables
+
+Example:
+
+```bash
+export INPUT_HOST="192.168.1.100"
+export INPUT_USERNAME="testuser"
+export INPUT_PASSWORD="testpass"
+export INPUT_PORT="22"
+export INPUT_SCRIPT="whoami"
+export GITHUB_ACTION_PATH="$(pwd)"
+./entrypoint.sh
+```
+
+## Important Patterns
+
+### Script Execution
+
+Users can provide scripts in two ways:
+
+- `script`: Inline commands (via `INPUT_SCRIPT`)
+- `script_path`: Path to a file in the repository (via `INPUT_SCRIPT_FILE`)
+
+### Error Handling
+
+To stop execution on first error (mimics removed `script_stop` option), users should add `set -e` to their scripts:
+
+```yaml
+script: |
+  #!/usr/bin/env bash
+  set -e
+  command1
+  command2
+```
+
+### Environment Variables
+
+The action passes GitHub Action inputs as environment variables with `INPUT_*` prefix. The drone-ssh binary reads these to configure SSH behavior.
+
+Special handling:
+
+- `envs`: Comma-separated list of environment variables to pass to remote script
+- `allenvs`: Pass all `GITHUB_*` and `INPUT_*` variables
+- `envs_format`: Custom format for environment variable export (e.g., `export TEST_{NAME}={VALUE}`)
+
+### Multiple Hosts
+
+- Comma-separated hosts: `"host1,host2"` (executes in parallel by default)
+- With custom ports: `"host1:2222,host2:5678"`
+- Synchronous execution: Set `sync: true`
+
+## Common Issues
+
+### Command Not Found
+
+Non-interactive shells may skip `.bashrc`/`.bash_profile`. See README section "Command not found" for details. Solutions:
+
+- Use absolute paths in commands
+- Comment out early return in `/etc/bash.bashrc`
+
+### OpenSSH Compatibility
+
+Ubuntu 20.04+ may require enabling `ssh-rsa` algorithm in sshd_config:
+
+```txt
+CASignatureAlgorithms +ssh-rsa
+```
+
+Or use ED25519 keys instead (preferred).
+
+## Development Guidelines
+
+### Adding New Parameters
+
+1. Add input definition to `action.yml` with description
+2. Add corresponding `INPUT_*` environment variable mapping in `action.yml` runs.steps
+3. Update README.md parameter tables
+4. The drone-ssh binary handles the actual parameter logic (separate repo)
+
+### Documentation
+
+- Keep parameter tables in README.md synchronized with `action.yml`
+- Maintain Chinese translations (README.zh-cn.md, README.zh-tw.md)
+- Use clear examples for each feature
+
+### Version Management
+
+The action pins to specific drone-ssh versions via:
+
+- Default: `DRONE_SSH_VERSION="1.8.1"` in `entrypoint.sh`
+- Override: Users can specify `version` input parameter
+
+Update the default version when new drone-ssh releases are available.
+
+## Release Process
+
+This action uses semantic versioning with major version tags:
+
+- Tags: `v1.0.0`, `v1.0.1`, etc.
+- Major version tag: `v1` (points to latest v1.x.x)
+- Users reference: `uses: appleboy/ssh-action@v1`
+
+GoReleaser config (`.goreleaser.yaml`) is present but set to `skip: true` since this action doesn't build Go code - it downloads pre-built binaries.