Add Railway/Nixpacks build config (requirements.txt, nixpacks.toml, runtime.txt)

Pure-stdlib repo had no language signal, so Nixpacks failed to build an image.
requirements.txt (empty) triggers Python detection; nixpacks.toml pins python311
and sets the start command to the webhook receiver.

nixpacks.toml

@@ -0,0 +1,6 @@
+# Explicit build config for Railway/Nixpacks (pure-stdlib Python service)
+[phases.setup]
+nixPkgs = ["python311"]
+
+[start]
+cmd = "python3 webhook_receiver.py"

requirements.txt

@@ -0,0 +1,2 @@
+# Winning Wallet Finder — no third-party deps, Python 3 stdlib only.
+# This file exists so Railway/Nixpacks detects a Python app.

runtime.txt

@@ -0,0 +1 @@
+3.11