feat: add editable channel images

docs/FEATURES/channels.md

@@ -14,6 +14,8 @@ A channel has:
 - `network`
 - optional `handle`
 - optional `externalUrl`
+- optional `portraitUrl`
+- optional `bannerUrl`
 - `createdAt`
 
 `network` is a controlled string matching the frontend channel network options:
@@ -33,6 +35,7 @@ Channel names must be unique inside a workspace for the same network.
 
 - Authenticated users with workspace access can list channels for their active workspace.
 - Workspace managers can create channels.
+- Workspace managers can edit channel profile fields and upload portrait/banner images.
 - Content planning uses configured channels as selectable destinations.
 - Development seed data should create real workspace channels instead of relying on content target labels as fake channels.