Add Railway deployment config — Procfile, runtime.txt, nixpacks.toml

Procfile

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+web: uvicorn app.main:app --host 0.0.0.0 --port ${PORT:-8000}

nixpacks.toml

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+[phases.setup]
+nixPkgs = ["python311", "gcc"]
+
+[phases.install]
+cmds = ["pip install -r requirements.txt"]
+
+[start]
+cmd = "uvicorn app.main:app --host 0.0.0.0 --port ${PORT:-8000}"

runtime.txt

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+python-3.11.15