fix: start codex on Windows by using shell; keep mcp args parseable (#40)

Windows global installs expose codex as codex.cmd; spawning 'codex' without shell hits ENOENT.

Enable shell to align with Claude's Windows behavior and resolve PATH lookup.

Shell spawn makes cmd.exe strip TOML double quotes in -c arrays, so args become a string.

Switch mcp args to TOML literal (single-quoted) arrays to preserve types; update tests.

cli/src/codex/utils/codexMcpConfig.test.ts

@@ -15,7 +15,7 @@ describe('codexMcpConfig', () => {
 
             expect(args).toEqual([
                 '-c', 'mcp_servers.hapi.command="hapi"',
-                '-c', 'mcp_servers.hapi.args=["mcp","--url","http://localhost:3000"]'
+                '-c', "mcp_servers.hapi.args=['mcp','--url','http://localhost:3000']"
             ]);
         });