Add fpp-sled-mailbox plugin

[focusedonsound]

Sensor-driven video playback / Santa Mailbox plugin for FPP — GPIO letter/donation sensors, HLK-LD2410B radar car detection, MQTT/Home Assistant integration, SQLite-backed analytics dashboard.

Repo: https://github.com/focusedonsound/fpp-sled-mailbox
pluginInfo.json: https://raw.githubusercontent.com/focusedonsound/fpp-sled-mailbox/refs/heads/main/pluginInfo.json

Single-line addition to pluginList.json, no other formatting changes.

[darylc]

Hi @focusedonsound. Due to the large number of AI generated plugins being submitted to FPP this year. We are having a pause at the moment whilst we establish updated guidelines for plugin submission, plugin structure in FPP, the plugin json file and the intake process. We will tag you when the information is released over the next few weeks.

[focusedonsound]

Thanks for the update — makes sense given the volume you're dealing with, happy to wait for the new process.

For reference whenever review picks back up: I did a walkthrough of all three plugins (this one, fpp-hdmi-cec, and the already-merged fpp-AnnouncementAssistant) on an xLights Gems session, in case it's useful context on what they do and how they work: https://www.youtube.com/watch?v=FfLZP2s3b60