fix: clarify agent terminal tool guidance

[myro2002]

Summary

• distinguish persistent interactive terminals from one-shot shell commands and background jobs
• document session cwd/ownership and terminal lifecycle
• correct Windows Ctrl+C, Ctrl+Z, and termination semantics
• clarify non-blocking reads versus blocking waits
• add description-contract coverage

Testing

• focused tool-description assertions added in tests/tools.spec.ts
• full local package gates should run in CI

[myro2002]

Closing at the author's request; the change will be maintained locally instead.