feat: add dashboard ping button and .env file support

Add a "Send IRC Message" section to the admin dashboard that sends a
configurable privmsg to any IRC nick or channel via all connected bots.
New POST /admin/ping endpoint broadcasts a "privmsg" WebSocket message
type, handled by both Limnoria and Sopel plugins.

Also enable pydantic-settings .env file loading (python-dotenv) and
add .env.example documenting all NTR_* configuration variables.

Made-with: Cursor

plugins/sopel/ntr_playlist.py

@@ -95,6 +95,9 @@ def _ws_listener(bot):
                     if data.get("type") == "announce" and "message" in data:
                         bot.say(data["message"], channel)
                         LOGGER.info("Announced to %s: %s", channel, data["message"])
+                    elif data.get("type") == "privmsg" and "target" in data and "message" in data:
+                        bot.say(data["message"], data["target"])
+                        LOGGER.info("Sent privmsg to %s: %s", data["target"], data["message"])
                     elif data.get("type") == "status":
                         LOGGER.info(
                             "Status update: %d bot(s) connected, clients=%s",