Add Web Admin Dashboard, JSON API, and Basic Auth

[NangenX]

Description:
This PR introduces a lightweight, embedded web administration dashboard to monitor the server status, stream hubs, and connected clients in real-time. It adheres to the "lite" philosophy of the project by requiring no external dependencies or extra files.

Key Features:

Web Dashboard (/admin):

A modern, dark-themed, single-page interface embedded directly into the binary.
Real-time monitoring (1s refresh rate) of CPU, RAM, and Network I/O.
Detailed view of Stream Hubs, including source addresses (UDP/RTP) and input bitrates.
Expandable client lists showing Client IP, User Agent, and connection duration.
JSON API (/api/stats):

New endpoint providing structured system and stream data in JSON format.
Implemented without external JSON libraries to maintain zero dependencies.
Basic Authentication:

Added support for HTTP Basic Authentication to protect the /admin and /api/stats endpoints.
Configurable via msd_lite.conf.
Configuration Changes:
To enable Basic Authentication, add the following section to msd_lite.conf inside the tag:

<msd>
    ...
    <admin>
        <user>admin</user>
        <password>your_secure_password</password>
    </admin>
    ...
</msd>

[rozhuk-im]

There is base64 encoder/decoder in liblcb: /include/utils/base64.h

[rozhuk-im]

There is mem_replace_arr() for things like that, or at least switch() is better.

[rozhuk-im]

Awesome work!