Add Chat Pulse add-on

[sravan1023]

Adds Chat Pulse, a live chat statistics add-on.

• A messages-per-minute badge under the player, refreshed every second.
• Clicking it opens a popup with session totals (messages, unique chatters, emote-only share), a five-minute activity sparkline, top chatters, top emotes, and a reset button.
• Settings under Add-Ons > Chat Pulse: show or hide the badge, rate window, whether to count pre-join history, and top list length.

A chat tokenizer at priority 0 counts each message once per room. Stats are kept in memory for the page session only. No external requests.