refactor(types): strengthen Zod schemas with regex validation and derive CalendarEvent

Add regex-based data URL validation for images, compute binary size
from base64 for accurate 10MB limit, enforce datetime strings with
offset for start/end fields, and derive CalendarEvent from the AI
response item type to eliminate field duplication.

src/lib/types.ts

@@ -1,12 +1,26 @@
 import { z } from "zod";
+import { MAX_IMAGE_SIZE_BYTES } from "@/lib/constants";
+
+/** Validates that a base64 data URL string decodes to binary under the max size. */
+const isValidImageSize = (val: string | undefined): boolean => {
+	if (!val) return true;
+	const base64Part = val.split(",")[1] ?? "";
+	const binarySize = Math.ceil(base64Part.length * 0.75);
+	return binarySize <= MAX_IMAGE_SIZE_BYTES;
+};
 
 export const AiEventRequestSchema = z
 	.object({
 		prompt: z.string().trim().max(2000).optional(),
 		imageBase64: z
 			.string()
-			.startsWith("data:", "Must be a valid data URL")
+			.regex(
-			.max(10 * 1024 * 1024 * 1.37, "Image must be less than 10MB")
+				/^data:image\/(png|jpeg|webp);base64,/,
+				"Must be a valid image data URL (PNG, JPEG, or WebP)",
+			)
+			.refine(isValidImageSize, {
+				message: "Image must be less than 10MB",
+			})
 			.optional(),
 	})
 	.refine((data) => data.prompt || data.imageBase64, {
@@ -21,25 +35,18 @@ export const AiEventResponseItemSchema = z.object({
 	description: z.string().optional(),
 	location: z.string().optional(),
 	url: z.string().optional(),
-	start: z.string(),
+	start: z.string().datetime({ offset: true }),
-	end: z.string().optional(),
+	end: z.string().datetime({ offset: true }).optional(),
 	allDay: z.boolean().optional(),
 	recurrenceRule: z.string().optional(),
 });
 
 export const AiEventResponseSchema = z.array(AiEventResponseItemSchema);
 
-export type CalendarEvent = {
+export type AiEventResponseItem = z.infer<typeof AiEventResponseItemSchema>;
+
+export type CalendarEvent = AiEventResponseItem & {
 	id: string;
-	title: string;
-	description?: string;
-	location?: string;
-	url?: string;
-	start: string;
-	end?: string;
-	allDay?: boolean;
 	createdAt?: string;
 	lastModified?: string;
-
-	recurrenceRule?: string;
 };