Honor WEB_SHELL_CWD env var for new shell cwd

Lets deployers (e.g. the Coder module) point new sessions at a
specific working directory without needing to pass cwd through the
create-session API.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: chapterjason

package.json

@@ -1,6 +1,6 @@
 {
   "name": "web-shell",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "private": true,
   "type": "module",
   "main": "server/dist/index.js",

server/src/utils/shell.ts

@@ -5,5 +5,5 @@ export function defaultShell(): string {
 }
 
 export function defaultCwd(): string {
-  return process.env["HOME"] ?? process.cwd();
+  return process.env["WEB_SHELL_CWD"] ?? process.env["HOME"] ?? process.cwd();
 }