feat: Allow setting port as PORT env var

This seems important for render hosting, as described in
https://render.com/docs/web-services#port-binding.

prophet/app.py

@@ -8,6 +8,7 @@ from fastapi.staticfiles import StaticFiles
 from fastapi_utils.tasks import repeat_every
 
 from prophet import view
+from prophet.config import AppConfig
 from prophet.domain.improvement import Improvement
 from prophet.domain.improvement_repo import IImprovementRepo
 from prophet.domain.original import Original
@@ -135,7 +136,9 @@ async def fetch_update(debug_print: bool = True):
 def start() -> None:
     from uvicorn import run
 
-    run("prophet.app:app", reload=True, host="0.0.0.0")
+    config = AppConfig.from_env()
+
+    run("prophet.app:app", reload=True, host="0.0.0.0", port=config.PORT)
 
 
 if __name__ == "__main__":

prophet/config.py

@@ -8,6 +8,16 @@ from dotenv import load_dotenv
 _ = load_dotenv()
 
 
+@dataclass
+class AppConfig:
+    PORT: int
+
+    @classmethod
+    def from_env(cls) -> "AppConfig":
+        PORT = os.getenv("PORT", "8000")
+        return cls(PORT=int(PORT))
+
+
 @dataclass
 class AiConfig:
     API_KEY: str