Update CI configuration and streamline terminal input handling

[OutOfBedlam]

This pull request updates the CI configuration to use newer macOS runners and refactors the way terminal control is handled for child processes in the Unix engine. The main focus is improving platform compatibility and streamlining terminal management during command execution.

Platform compatibility:

• Updated the CI workflow to use macos-26 and macos-26-intel runners instead of the deprecated macos-15 and macos-15-intel runners in .github/workflows/ci-main.yml. This ensures our builds and tests run on the latest available macOS environments.

Terminal control handling:

• Moved the logic for setting the child process as the foreground process group (using syscall.SYS_IOCTL with syscall.TIOCSPGRP) earlier in the exec0 function in jsh/engine/engine_unix.go. This change ensures the child process receives terminal control before signal forwarding and other setup, improving correctness and reliability when running interactive commands. [1] [2]

[codecov]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.76%. Comparing base (8dc8edc) to head (d01e4e5).

Files with missing lines	Patch %	Lines
jsh/engine/engine_unix.go	0.00%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #410   +/-   ##
=======================================
  Coverage   63.76%   63.76%           
=======================================
  Files         352      352           
  Lines       68892    68892           
=======================================
  Hits        43929    43929           
  Misses      20345    20345           
  Partials     4618     4618           

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