Fix env loading to skip unexpanded shell variables

Skip entries containing $ in setup_environment() to prevent PATH being
overwritten with literal "$PATH" string from ~/.env

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: wenaus

src/swf_common_lib/base_agent.py

@@ -53,8 +53,13 @@ def setup_environment():
                     if line.startswith('export '):
                         line = line[7:]  # Remove 'export '
                     key, value = line.split('=', 1)
-                    os.environ[key] = value.strip('"\'')
-    
+                    value = value.strip('"\'')
+                    # Skip entries with unexpanded shell variables (e.g., PATH=$PATH:...)
+                    # These are already expanded by shell when it sourced ~/.env
+                    if '$' in value:
+                        continue
+                    os.environ[key] = value
+
     # Unset proxy variables to prevent localhost routing through proxy
     for proxy_var in ['http_proxy', 'https_proxy', 'HTTP_PROXY', 'HTTPS_PROXY']:
         if proxy_var in os.environ: