[FEATURE] Allow explicit SSH binary path configuration on Windows

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

On Windows, Claude Code Desktop resolves the SSH binary from the system PATH.
However, many developers have multiple SSH implementations installed simultaneously:

• Win32-OpenSSH: C:\Windows\System32\OpenSSH\ssh.exe

-> integrates with Windows OpenSSH Authentication Agent (ssh-agent service)

• Git for Windows: C:\Program Files\Git\usr\bin\ssh.exe

-> uses its own MSYS2-based agent, does NOT integrate with Win32 ssh-agent

Claude Code's own documentation and VS Code integration recommend Git for Windows,
which means many users have Git for Windows' ssh.exe appearing earlier in PATH.
This creates a conflict: the SSH binary actually used by Claude Code Desktop
is PATH-order dependent and not visible anywhere in the UI.

Impact

Users who want to use ssh-agent with a passphrase-protected key face this specific
problem:

1. They start Windows OpenSSH Authentication Agent service
2. They run ssh-add to register their key (passphrase entered once)
3. Claude Code Desktop silently picks up Git for Windows' ssh.exe instead
4. Git for Windows' ssh.exe does not talk to Win32 ssh-agent -> authentication fails

There is currently no way to guarantee which SSH binary Claude Code Desktop uses
without manipulating system PATH order -- a fragile, user-invisible workaround.

Proposed Solution

Add a configurable sshExecutablePath setting, for example in
~/.claude/settings.json:

{
  "ssh": {
    "executablePath": "C:\\Windows\\System32\\OpenSSH\\ssh.exe"
  }
}

Or expose it in the Desktop UI's SSH connection settings dialog.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Use Case Example

_No response_

Additional Context

Environment

• Windows 11
• Git for Windows installed (as recommended by Claude Code docs)
• Win32-OpenSSH installed
• Claude Desktop (latest)

Related Issues

• #25659 / #26116 (hardcoded /usr/bin/ssh — already fixed)