Use local timezone for ISO date to avoid midnight inconsistency

toISOString() returns UTC which can differ from the local date near
midnight, causing contradictory dates in the same prompt (e.g. the
human-readable date says "February 25" while the ISO date says
"2026-02-26"). Build the ISO string from local date components instead
so all date values in the tool preprompt stay consistent.

https://claude.ai/code/session_01DmqK4Lmm7Uv41oHV3HqWpT

Author: claude

src/lib/server/textGeneration/utils/toolPrompt.ts

@@ -12,7 +12,7 @@ export function buildToolPreprompt(tools: OpenAiTool[]): string {
 		month: "long",
 		day: "numeric",
 	});
-	const isoDate = now.toISOString().split("T")[0];
+	const isoDate = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-${String(now.getDate()).padStart(2, "0")}`;
 	return [
 		`You have access to these tools: ${names.join(", ")}.`,
 		`Today's date: ${currentDate} (${isoDate}).`,