feat(types): add base AJAXRequest type definitions

[usernane]

Summary

Adds dist/ajaxrequest.d.ts — complete TypeScript type definitions for the AJAXRequest class.

What's included

Class declaration:

• Constructor with AJAXRequestConfig parameter
• Static properties: META, CALLBACK_POOLS, BACKOFF
• Static methods: createXhr(), extractBase(), isValidURL()
• All instance methods (getters, setters, callback registration/management, retry, send)
• Deprecated methods marked with @deprecated

Interfaces:

• AJAXRequestConfig — constructor configuration
• AJAXResponse — Promise resolve/reject shape
• RetryConfig — object-form retry configuration
• CallbackContext, BeforeAjaxContext, ErrorCallbackContext, RetryCallbackContext, RetryEndCallbackContext — this context types for callbacks
• CallbackObject — object-form callback with id/call/props
• AJAXRequestMeta, BackoffEnum

Type aliases:

• HttpMethod, CallbackPoolName, BackoffStrategy, CallbackParam
• ResponseCallback, BeforeAjaxCallback, AJAXErrorCallback, RetryCallback, RetryEndCallback

Global:

• declare const ajax: AJAXRequest for UMD/script tag users

Validation

• tsc --noEmit --strict passes with zero errors
• Tested with a consumer file covering: constructor, static access, all methods, callbacks with typed this, retry config, Promise return type

Notes

• ErrorCallback renamed to AJAXErrorCallback to avoid conflict with lib.dom.d.ts
• Module export support will be added in feat(types): add callback types #101/feat(types): add config object types #102

Closes #100