Document Comp Channels, News, and manager role Adds the comp-channel system (public /files/channels/, admin /accounts/admin/channels/*, per-channel memberships, channel-scoped proposal/comp-proposal endpoints), the manager_enabled admin flag, and a new News page (/news/* feed, channels, attachments) now that the backend has shipped both. Corrects Auth & Accounts' Permission Matrix and role table to include Manager and is_news, and adds the previously-undocumented /files/list-all/, /files/thumbnail/, and /files/zip-selection/ endpoints.