refactor: update diagnostic messages for query validation in missing and null plugins

apps/infoalloggi/biome_plugins/missing.grit

@@ -20,6 +20,6 @@ language js
 			$fn <: contains `executeTakeFirstOrThrow`
 		},
 		! $fn <: contains `where`,
-		register_diagnostic(span=$fn, message="where or delete statements must contain where()", severity="error")
+		register_diagnostic(span=$fn, message="update or delete statements must contain where()", severity="error")
 	}
 }

apps/infoalloggi/biome_plugins/null.grit

@@ -9,5 +9,5 @@ language js
 		$a <: contains `'!=='`
 	},
 	$a <: contains `null`,
-	register_diagnostic(span=$a, message=$a, severity="error")
+	register_diagnostic(span=$a, message="Comparisons to null using '=' or '==' are not allowed. Use 'is' or 'is not' instead.", severity="error")
 }