chore: upgrade Zod 4, Vitest 4, and TypeScript 7

Bump major tooling stacks and adapt Zod error APIs (issues/flattenError) plus tsconfig paths for TS 7 baseUrl removal.

Co-authored-by: Cursor <[email protected]>

src/env.ts

@@ -86,7 +86,7 @@ const schema = z.object({
 	if (data.NODE_ENV !== "production") return;
 	if (!data.AUTH_SECRET || data.AUTH_SECRET.length < 32) {
 		ctx.addIssue({
-			code: z.ZodIssueCode.custom,
+			code: "custom",
 			message:
 				"AUTH_SECRET (>=32 characters) is required when NODE_ENV=production",
 			path: ["AUTH_SECRET"],