refactor: update environment variable constants and usage in gateway

pkg/config/envkeys.go

@@ -30,4 +30,8 @@ const (
 	// Used by the web launcher when spawning the gateway subprocess.
 	// Default: resolved from the same directory as the current executable.
 	EnvBinary = "PICOCLAW_BINARY"
+
+	// EnvGatewayHost overrides the host address for the gateway server.
+	// Default: "127.0.0.1"
+	EnvGatewayHost = "PICOCLAW_GATEWAY_HOST"
 )

pkg/migrate/sources/openclaw/openclaw_handler.go

@@ -1,10 +1,5 @@
 package openclaw
 
-// OpenclawHomeEnvVar is the environment variable that overrides the source
-// openclaw home directory when migrating from openclaw to picoclaw.
-// Default: ~/.openclaw
-const OpenclawHomeEnvVar = "OPENCLAW_HOME"
-
 import (
 	"fmt"
 	"os"
@@ -15,6 +10,11 @@ import (
 	"github.com/sipeed/picoclaw/pkg/migrate/internal"
 )
 
+// OpenclawHomeEnvVar is the environment variable that overrides the source
+// openclaw home directory when migrating from openclaw to picoclaw.
+// Default: ~/.openclaw
+const OpenclawHomeEnvVar = "OPENCLAW_HOME"
+
 var providerMapping = map[string]string{
 	"anthropic":  "anthropic",
 	"claude":     "anthropic",

pkg/providers/codex_cli_credentials.go

@@ -1,10 +1,5 @@
 package providers
 
-// CodexHomeEnvVar is the environment variable that overrides the Codex CLI
-// home directory when resolving the codex auth.json credentials file.
-// Default: ~/.codex
-const CodexHomeEnvVar = "CODEX_HOME"
-
 import (
 	"encoding/json"
 	"fmt"
@@ -13,6 +8,11 @@ import (
 	"time"
 )
 
+// CodexHomeEnvVar is the environment variable that overrides the Codex CLI
+// home directory when resolving the codex auth.json credentials file.
+// Default: ~/.codex
+const CodexHomeEnvVar = "CODEX_HOME"
+
 // CodexCliAuth represents the ~/.codex/auth.json file structure.
 type CodexCliAuth struct {
 	Tokens struct {

web/backend/api/gateway.go

@@ -387,10 +387,10 @@ func (h *Handler) startGatewayLocked(initialStatus string, existingPid int) (int
 	// GetConfigPath() already reads, so the gateway sub-process uses the same
 	// config file without requiring a --config flag on the gateway subcommand.
 	if h.configPath != "" {
-		cmd.Env = append(cmd.Env, "PICOCLAW_CONFIG="+h.configPath)
+		cmd.Env = append(cmd.Env, config.EnvConfig+"="+h.configPath)
 	}
 	if host := h.gatewayHostOverride(); host != "" {
-		cmd.Env = append(cmd.Env, "PICOCLAW_GATEWAY_HOST="+host)
+		cmd.Env = append(cmd.Env, config.EnvGatewayHost+"="+host)
 	}
 
 	stdoutPipe, err := cmd.StdoutPipe()