docs: 📝 Add documentation for entities

app/types/page.mdx

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+
+## ISO8601
+
+```typescript
+type Year = `${number}${number}${number}${number}`;
+type Month = `${"0" | "1"}${number}`;
+type Day = `${"0" | "1" | "2" | "3"}${number}`;
+
+type DateString = `${Year}-${Month}-${Day}`;
+
+type Hour = `${"0" | "1" | "2"}${number}`;
+type Minute = `${"0" | "1" | "2" | "3" | "4" | "5"}${number}`;
+type Second = `${"0" | "1" | "2" | "3" | "4" | "5"}${number}`;
+
+type TimeString = `${Hour}:${Minute}:${Second}`;
+
+type Offset = `${"Z" | "+" | "-"}${Hour}:${Minute}`;
+
+type ISO8601 = `${DateString}T${TimeString}${Offset}`;
+```
+
+## UUID
+
+```typescript
+type UUID = `${number}-${number}-${number}-${number}-${number}`;
+```
+
+## URI
+
+```typescript
+type URI = string;
+```
+
+## Extensions
+
+```typescript
+type OrgNamespace = string;
+type ExtensionName = string;
+
+type ExtensionsKey = `${OrgNamespace}:${ExtensionName}`;
+
+type Extensions = {
+    [key in ExtensionsKey]: any;
+}
+```