fix: add pyproject.toml for openenv validate

server/app.py

@@ -2,26 +2,38 @@
 server/app.py — OpenEnv required server entry point.
 Delegates to the main FastAPI application.
 """
-import uvicorn
-import sys
 import os
+import sys
+import uvicorn
 
-# Ensure project root is on path
+# Ensure project root is on path before local imports
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 from app.main import app  # noqa: F401 — re-exported for openenv
 
+# Named Constants
+DEFAULT_HOST = "0.0.0.0"
+DEFAULT_PORT = 7860
+DEFAULT_WORKERS = 2
+
+
+def main() -> None:
+    """Entry point for [project.scripts] server = 'server.app:main'"""
+    port_str: str = os.environ.get("PORT", str(DEFAULT_PORT))
+    
+    try:
+        port_num: int = int(port_str)
+    except ValueError as e:
+        raise ValueError(f"Invalid PORT environment variable: '{port_str}'. Must be an integer.") from e
 
-def start():
-    """Entry point for [project.scripts] server = 'server.app:start'"""
     uvicorn.run(
         "app.main:app",
-        host="0.0.0.0",
-        port=int(os.environ.get("PORT", 7860)),
-        workers=2,
+        host=DEFAULT_HOST,
+        port=port_num,
+        workers=DEFAULT_WORKERS,
         log_level="info",
     )
 
 
 if __name__ == '__main__':
-    start()
+    main()