Add gunicorn, fix binding to 0.0.0.0:$PORT for Railway health checks

Author: level09

nixpacks.toml

@@ -3,4 +3,5 @@
 # This overrides the start command to use gunicorn (which auto-binds to $PORT)
 
 [start]
-cmd = "gunicorn run:app --workers 2 --threads 2"
+# Bind to Railway-provided $PORT and all interfaces so health checks can reach the app
+cmd = "gunicorn run:app --workers 2 --threads 2 --bind 0.0.0.0:${PORT}"

pyproject.toml

@@ -60,6 +60,7 @@ dependencies = [
     "python-editor>=1.0.4",
     # Production server
     "uwsgi>=2.0.30; sys_platform != 'win32'",
+    "gunicorn>=23.0.0",
     "sluggi>=0.1.1",
     # Payments and billing
     "stripe>=12.0.0",