Argon2id:
- Increase memory parameter from 64 MiB to 128 MiB for stronger KDF
SSH Agent:
- Add agent.go with connectAgent(), agentAuthMethod(), requestAgentForwarding()
- Integrate agent auth into buildAuthMethods() (tried first when enabled)
- Set up agent forwarding after PTY allocation when agentForwarding is true
- Track and clean up agent socket connection on session close
- Add AgentAuth and AgentForwarding fields to SSHConfig model
- Add SSH Agent section to profile editor with toggle controls
