add: /debug/config endpoint to check env vars

Visit https://memverge-memprepmate.hf.space/debug/config
to see actual environment variable values

src/app.py

@@ -168,6 +168,26 @@ def create_app():
     def health():
         """Health check endpoint for monitoring."""
         return jsonify({"status": "ok"}), 200
+    
+    # Diagnostic endpoint to check environment variables
+    @app.route("/debug/config")
+    def debug_config():
+        """Show current configuration for debugging."""
+        return jsonify({
+            "environment_variables": {
+                "SESSION_COOKIE_SECURE": os.getenv("SESSION_COOKIE_SECURE", "NOT SET"),
+                "SESSION_COOKIE_SAMESITE": os.getenv("SESSION_COOKIE_SAMESITE", "NOT SET"),
+                "PREFERRED_URL_SCHEME": os.getenv("PREFERRED_URL_SCHEME", "NOT SET"),
+                "SECRET_KEY": "SET" if os.getenv("SECRET_KEY") else "NOT SET",
+            },
+            "flask_config": {
+                "SESSION_COOKIE_SECURE": app.config.get("SESSION_COOKIE_SECURE"),
+                "SESSION_COOKIE_SAMESITE": str(app.config.get("SESSION_COOKIE_SAMESITE")),
+                "SESSION_COOKIE_NAME": app.config.get("SESSION_COOKIE_NAME"),
+                "SESSION_COOKIE_PATH": app.config.get("SESSION_COOKIE_PATH"),
+                "PREFERRED_URL_SCHEME": app.config.get("PREFERRED_URL_SCHEME"),
+            }
+        }), 200
 
     return app