fix: make .zprofile SSH agent setup fail-safe

- Create ~/.ssh dir if missing before writing agent-environment
- Suppress ssh-add errors (no keys yet is fine)
- Skip entire block if ssh-agent binary is not installed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.zprofile

@@ -2,20 +2,25 @@ SSH_ENV="$HOME/.ssh/agent-environment"
 
 function start_agent {
     echo "Initialising new SSH agent..."
+    mkdir -p "$HOME/.ssh"
+    chmod 700 "$HOME/.ssh"
     /usr/bin/ssh-agent | sed 's/^echo/#echo/' >"$SSH_ENV"
     echo succeeded
     chmod 600 "$SSH_ENV"
     . "$SSH_ENV" >/dev/null
-    /usr/bin/ssh-add;
+    /usr/bin/ssh-add 2>/dev/null || true
 }
 
-# Source SSH settings, if applicable
+# Source SSH settings, if applicable — skip entirely if ssh-agent is not available
+if ! command -v ssh-agent >/dev/null 2>&1; then
+    return 0
+fi
+
 if [ -f "$SSH_ENV" ]; then
     . "$SSH_ENV" >/dev/null
-    #ps $SSH_AGENT_PID doesn't work under Cygwin
     ps -ef | grep $SSH_AGENT_PID | grep ssh-agent$ >/dev/null || {
         start_agent
     }
 else
     start_agent
-fi
+fi