feat: bootstrap FastAPI configuration

app/main.py

@@ -0,0 +1,22 @@
+from fastapi import FastAPI
+
+from app.config import Settings, get_settings
+
+
+def create_app(settings: Settings | None = None) -> FastAPI:
+    resolved = settings or get_settings()
+    resolved.data_dir.mkdir(parents=True, exist_ok=True)
+    resolved.tokens_dir.mkdir(parents=True, exist_ok=True)
+    resolved.activities_dir.mkdir(parents=True, exist_ok=True)
+
+    app = FastAPI(title="MyWhoosh Garmin Sync")
+    app.state.settings = resolved
+
+    @app.get("/healthz")
+    def healthz() -> dict[str, str]:
+        return {"status": "ok"}
+
+    return app
+
+
+app = create_app()