feat(config): Add support for env var configuration (#896)

* feat(config): Add support for env var configuration

This commit introduces support for two environment variables,
allowing users to override the default paths for picoclaw's home
directory and configuration file.

- `PICOCLAW_CONFIG`: Directly specifies the path to the `config.json` file.
This is initialised first, takes precedence over the hardcoded path, and is ideal
for containerized deployments or custom config management.

- `PICOCLAW_HOME`: Overrides the root directory for all picoclaw data, (except the config)
(e.g., `~/.picoclaw`). This is useful for portable installations or placing
data in non-standard locations.

This change provides greater flexibility for running picoclaw in various environments without
being tied to the default home directory structure.

* `README.md` updated explain PICOCLAW_CONFIG and PICOCLAW_HOME

* docs: translate environment variables section to multiple languages

---------

Co-authored-by: picoclaw <picoclaw@sipeed.com>

cmd/picoclaw/internal/helpers.go

@@ -19,6 +19,9 @@ var (
 )
 
 func GetConfigPath() string {
+	if configPath := os.Getenv("PICOCLAW_CONFIG"); configPath != "" {
+		return configPath
+	}
 	home, _ := os.UserHomeDir()
 	return filepath.Join(home, ".picoclaw", "config.json")
 }

cmd/picoclaw/internal/helpers_test.go

@@ -95,3 +95,13 @@ func TestGetConfigPath_Windows(t *testing.T) {
 func TestGetVersion(t *testing.T) {
 	assert.Equal(t, "dev", GetVersion())
 }
+
+func TestGetConfigPath_WithEnv(t *testing.T) {
+	t.Setenv("PICOCLAW_CONFIG", "/tmp/custom/config.json")
+	t.Setenv("HOME", "/tmp/home") // Also set home to ensure env is preferred
+
+	got := GetConfigPath()
+	want := "/tmp/custom/config.json"
+
+	assert.Equal(t, want, got)
+}