Reduce window for time series to 2 days

2 weeks still seems to cause a timeout in production, so I'm going to
ratchet this way down just to see if I can get things working, and from
there we can see about what resources we need to get a wider window.

src/unified_graphics/diag.py

@@ -344,7 +344,7 @@ def history(
         variable.value,
     )
 
-    start = initialization_time - timedelta(weeks=2)
+    start = initialization_time - timedelta(days=2)
     df = pd.read_parquet(
         parquet_file,
         columns=["initialization_time", "obs_minus_forecast_unadjusted"],