Add --web flag to issue create to open in browser

Context

When creating an issue, it's often useful to immediately open it in the browser to verify it looks correct or to share the link. The gh CLI supports gh issue create --web for this purpose, and it's a convenient quality-of-life feature for human workflows.

Tasks

• Add --web / -w flag to tangled issue create.
  • After successful creation, open the issue URL in the default browser using Node's open package (or a lightweight equivalent).
  • The flag should be a no-op (silently ignored) in non-interactive / piped environments where opening a browser makes no sense.
• Add tests verifying the browser open is triggered when --open is passed and skipped otherwise.

Notes

Should not block or change the normal stdout output — the issue URL should still be printed as usual, and the browser open should happen as a side effect.