feat(ssh): add detailed SSH agent connection logging

[andya1lan]

Problem

Following the Windows OpenSSH agent support feature attached issue #2643 , users reported connection failures without any useful diagnostic information in the logs when connecting with SSH agent. This made troubleshooting difficult as there was no visibility into:

• SSH configuration being used
• Agent connection attempts and results
• Which keys were being tried
• Why connections failed Additionally, when logs were shared for debugging, they exposed sensitive information including full usernames, hostnames, file paths, and IP addresses.

Implementation

1. Enhanced SSH/Agent Logging

• Add logSSHKeywords() helper to log SSH config details for debugging
• Enhance agent connection/communication logging with blocklogger
• Use INFO level for key events:
  • Agent connect success/failure
  • Number of signers retrieved
  • Connection attempts and results
• Use DEBUG level for diagnostic details:
  • SSH config parameters
  • Key fingerprints
  • Config loading source
• Add Windows-specific hint when agent connection fails

2. Privacy Masking

• Add MaskString() utility: shows first 3 + last 3 characters (e.g., ubuntu@server → ubu***ver)
• Add maskIdentityFile(): masks usernames in paths while preserving structure
• Apply masking to all sensitive log data:
  • Usernames and hostnames
  • Connection identifiers (remoteName, connection options)
  • Network addresses (IP:port)
  • Known hosts addresses
  • Key fingerprints
  • Shell paths