Add llc.NextcloudCalendars to community plugins

[Bono2007]

Adds Agendas Nextcloud (llc.NextcloudCalendars) to community-plugins.json.

The plugin fetches shared CalDAV calendars from a Nextcloud server and writes a daily agenda block into calendar notes, several days ahead. It was built to follow colleagues' shared calendars, but works with any CalDAV server exposing a Nextcloud-style layout.

Repository: https://github.com/Bono2007/noteplan-nextcloud-calendars
Release: llc-nextcloudcalendars-v1.0.0

What it does

• Discovers the calendars available on the server and lets the user pick which ones to follow, with short auto-derived labels
• Writes an agenda block into each of the next N daily notes (7 by default), replacing it in place on every run without touching the rest of the note
• Expands recurring events server-side via <C:expand>, so a weekly meeting shows up on each occurrence
• Shows multi-day events on every day they span, and all-day events without a time
• Can be called from a template, returning the block without writing anything

Notes

• No npm dependencies. Sources in src/ are concatenated into a single standalone index.js by build.mjs.
• 117 tests run with node --test, including fixtures captured from a real server response.
• The plugin does not use the repository toolchain (Flow, Rollup, noteplan-cli), which is why it lives in its own repository and is referenced here rather than vendored in.

This PR only adds one entry to community-plugins.json.