feat: migrate displayed historical data to postgres

backend/app/main.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+from datetime import date, datetime
 from http import HTTPStatus
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 
@@ -38,7 +39,7 @@ class HealthHandler(BaseHTTPRequestHandler):
         return
 
     def _write_json(self, status: HTTPStatus, payload: dict[str, object]) -> None:
-        body = json.dumps(payload).encode("utf-8")
+        body = json.dumps(payload, default=_json_default).encode("utf-8")
         self.send_response(status)
         self._send_default_headers(content_length=len(body))
         self.end_headers()
@@ -61,6 +62,13 @@ def create_server() -> ThreadingHTTPServer:
     return ThreadingHTTPServer((host, port), HealthHandler)
 
 
+def _json_default(value: object) -> str:
+    """Serialize PostgreSQL date/time values before they can abort an HTTP response."""
+    if isinstance(value, (date, datetime)):
+        return value.isoformat()
+    raise TypeError(f"Object of type {type(value).__name__} is not JSON serializable")
+
+
 def run() -> None:
     """Start the local bootstrap server."""
     host, port = get_bind_address()