External Agent: Add Windows-compatible agent name derivation

[keyu98]

Summary

External agent discovery currently fails to correctly derive agent names on Windows because:

1. Windows executables have file extensions (.exe, .bat, .cmd) that get included in the agent name.
2. The Unix executable-bit check (mode & 0o111) rejects all binaries on Windows, since Windows doesn't set POSIX execute permission bits.

Changes

• Strip Windows executable extensions before deriving the agent name via a new stripExeExt() helper. This removes .exe, .bat, and .cmd suffixes so that entire-agent-foo.exe correctly resolves to agent name foo. On Unix this is a no-op.
• Skip the executable-bit check on Windows (runtime.GOOS != "windows"), since Windows filesystems do not expose POSIX permission bits.

Files changed

• cmd/entire/cli/agent/external/discovery.go

[nodo]

Thank you for the contribution @keyu98 ❤️ I have added a suggestion to simplify stripExeExt, also do you mind adding tests for it? The idea is great, just a couple of minor points.

[keyu98]

Thank you for the contribution @keyu98 ❤️ I have added a suggestion to simplify stripExeExt, also do you mind adding tests for it? The idea is great, just a couple of minor points.

Thanks for the review! I've simplified stripExeExt as suggested and added tests for it in the latest commit.

[nodo]

LGTM, please have a look at the failing test, then I am happy to approve.