[codex] fix Linux BrowserWindow focusable default

[zhuziqi97]

Summary

Fixes #29.

This adds a Linux upstream patch contract for the 26.623 BrowserWindow focus regression. Upstream changed the primary window options from omitting undefined focusable to passing focusable: undefined; Electron/Linux treats that as an unfocusable window, which can become an unmanaged override-redirect X11 surface and prevents normal input focus.

The patch rewrites only the primary BrowserWindow forwarding path from focusable:m to focusable:m??!0. Explicit focusable:false overlay/popup windows are preserved.

Validation

• node --test test/upstream-patches.test.mjs test/smoke-artifacts.test.mjs
• npm test
• Extracted the real 26.623.141536 main bundle from a local unpatched ASAR backup and verified patchUpstreamMainSource changes exactly one focusable default and leaves no unguarded focusable forwarding.
• node scripts/canary.mjs --channel prod --no-smoke --json-output dist/focusable-prod-canary.json
  • passed
  • appcast resolved prod 26.623.141536, build 4753, package 26.623.141536-launcher.33
• node scripts/release-channel.mjs --channel prod --archive .cache/prod/Codex-darwin-arm64-26.623.141536.zip --json-output dist/focusable-prod-build.json
  • passed and produced AppImage, unpacked tarball, checksums, npm package, and AUR files
• node scripts/canary.mjs --channel prod --no-browser --json-output dist/focusable-prod-canary-full.json
  • passed with artifact/desktop smoke enabled and only the browser shell smoke skipped
  • linux-window-focusable-contract passed with checked: 1

[cau1k]

LGTM. Thank you @zhuziqi97 !