docs(federation): 📝 Update SDK documentation

packages/sdk/schemas/entity.ts

@@ -0,0 +1,23 @@
+import { z } from "zod";
+import { isISOString } from "../regex.ts";
+import { url } from "./common.ts";
+import { CustomEmojiExtensionSchema } from "./extensions/emojis.ts";
+
+export const ExtensionPropertySchema = z
+    .object({
+        "pub.versia:custom_emojis":
+            CustomEmojiExtensionSchema.optional().nullable(),
+    })
+    .catchall(z.any());
+
+export const EntitySchema = z.strictObject({
+    // biome-ignore lint/style/useNamingConvention:
+    $schema: z.string().url().nullish(),
+    id: z.string().max(512),
+    created_at: z
+        .string()
+        .refine((v) => isISOString(v), "must be a valid ISO8601 datetime"),
+    uri: url,
+    type: z.string(),
+    extensions: ExtensionPropertySchema.nullish(),
+});