[Bug] TMPDIR not respecting environment variable, hardcoded to /tmp

Bug Description
TMPDIR hardcoded to /tmp , at least in node.js version. Thats not really cool because Unix systems support changing it with $TMPDIR variable for example. It reates an issues on environments with custom TMPDIR location.

Environment Info

• Platform: linux
• Terminal: xterm-256color
• Version: 2.1.14
• Feedback ID: cd5d24a4-ad8e-4e44-b24d-b2ccb40cee2d

Errors

[{"error":"Error: ENOENT: no such file or directory, scandir '/etc/claude-code/.claude/skills'\n    at readdirSync (unknown)\n    at <anonymous> (/$bunfs/root/claude:12:1903)\n    at eG (/$bunfs/root/claude:11:34695)\n    at readdirSync (/$bunfs/root/claude:12:1864)\n    at l4R (/$bunfs/root/claude:1463:380)\n    at l4R (/$bunfs/root/claude:1463:1350)\n    at <anonymous> (/$bunfs/root/claude:1463:4440)\n    at <anonymous> (/$bunfs/root/claude:1463:5171)\n    at A (/$bunfs/root/claude:11:7245)\n    at NW8 (/$bunfs/root/claude:4094:4342)","timestamp":"2026-01-21T07:10:29.731Z"},{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:47:10672)\n    at emit (node:events:92:22)\n    at <anonymous> (/$bunfs/root/claude:46:3314)\n    at request (/$bunfs/root/claude:49:2147)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-21T07:10:59.865Z"},{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:47:10672)\n    at emit (node:events:92:22)\n    at <anonymous> (/$bunfs/root/claude:46:3314)\n    at request (/$bunfs/root/claude:49:2147)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-21T07:11:06.837Z"},{"error":"Error: 1P event logging: 8 events failed to export\n    at queueFailedEvents (/$bunfs/root/claude:619:2077)\n    at async doExport (/$bunfs/root/claude:619:1257)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-21T07:12:03.528Z"},{"error":"Error: {\"message\":\"Failed to export 8 events\",\"originalLine\":\"619\",\"originalColumn\":\"1336\",\"line\":\"619\",\"column\":\"1336\",\"sourceURL\":\"/$bunfs/root/claude\",\"stack\":\"Error: Failed to export 8 events\\n    at doExport (/$bunfs/root/claude:619:1336)\\n    at processTicksAndRejections (native:7:39)\",\"name\":\"Error\"}\n    at error (/$bunfs/root/claude:2247:25028)\n    at <anonymous> (/$bunfs/root/claude:613:36349)\n    at hL0 (/$bunfs/root/claude:613:36893)\n    at <anonymous> (/$bunfs/root/claude:614:17366)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-21T07:12:03.528Z"}]