[rickypid]

Second release candidate of 2.0.0: message forwarding and a clean session
teardown on sign out. No database changes since rc.1.

Added

• SupabaseChatCore.forwardMessages: forwards messages to another room as
  new messages of the logged-in user, oldest first. Each copy stores its
  ChatForwardOrigin (original author and date) in the metadata and drops
  reply, reactions, pin and edited mark; chat attachments are copied into the
  destination room's folder.
• ChatForwardOrigin: reads the origin of a forwarded message
  (ChatForwardOrigin.of(message)).
• SupabaseChatCore.closeSession(): closes the own presence, room channels,
  presence watches and the roomsChanges/room/userOnlineStatus streams.
  Call it right before signing out, so private room channels leave cleanly
  instead of reporting subscription errors.

Changed

• Signing out or switching user closes the session automatically: the
  roomsChanges, room and userOnlineStatus streams complete instead of
  outliving the user, and SupabaseChatRoomsController clears its rooms
  (the next loadFirstPage listens again for the new user).
• ChatRoom equality compares every field, not only the id: a refetched
  room is no longer dropped as unchanged by lists and ValueNotifiers.
  Match rooms by id to find the same room.
• The example app calls closeSession() before signing out.
• README and documentation site cover forwarding, signing out and the
  session lifecycle.

Fixed

• Auth state changes arriving in bursts (initial session, signed in, token
  refreshed) could open the own presence channel twice.
• Late status callbacks of released room and presence channels changed the
  state of the current ones.
• Documentation site: "Edit this page" links, and links to the Flyer Chat
  2.x documentation instead of 1.x.