feat: add shared dashboard API contracts

packages/api-contracts/src/common.ts

@@ -0,0 +1,15 @@
+import { z } from 'zod';
+
+export const ErrorResponseSchema = z.strictObject({
+  error: z.string(),
+  detail: z.unknown().optional(),
+});
+
+export const SuccessResponseSchema = z.strictObject({ success: z.literal(true) });
+export const RejectedActionResponseSchema = z.strictObject({
+  success: z.literal(false),
+  reason: z.string(),
+});
+
+export type ErrorResponse = z.infer<typeof ErrorResponseSchema>;
+export type SuccessResponse = z.infer<typeof SuccessResponseSchema>;