feat(terminals): set PI WEB shell environment

[ongspxm]

Summary

Sets PI_WEB_TERMINAL=1 for all shells opened in PI WEB terminals, including continued interactive shells.

This lets users run shell startup scripts only inside PI WEB terminals, for example:

if [ "$PI_WEB_TERMINAL" = "1" ]; then
  # Run PI WEB terminal setup here
fi

Testing

• PI_WEB_TERMINAL=1 npm test -- --run src/server/terminals/terminalService.test.ts
• npm run typecheck
• npx eslint src/server/terminals/terminalService.ts src/server/terminals/terminalService.test.ts
• npm run verify
• npm run build
• npm run pack:dry

[jmfederico]

Thanks for the contribution. Merged! 🎉

Before merging, I made a few focused adjustments:

• Renamed IS_PIWEB to PI_WEB_TERMINAL to follow the existing PI_WEB_* convention and make its terminal-specific purpose explicit.
• Removed the root allowScripts entry because it was unrelated to this change and is not enforced by the project's current npm installation flow. It therefore did not approve the node-pty install script or change installation behavior.
• Strengthened the regression tests to cover both command terminals and continued interactive shells independently of the parent environment.

If dependency installation policy is still worth pursuing, please open a separate PR so its enforcement mechanism, package-manager support, documentation, and validation can be reviewed independently.

Thanks again!