docs: define organization account model

docs/PRODUCT.md

@@ -2,7 +2,7 @@
 
 Socialize is a workflow application for social media content review, revision, approval, and publication readiness.
 
-It is not a public social network. It is a workspace-based coordination tool for internal teams, providers, and client approvers.
+It is not a public social network. It is an organization-owned, workspace-based coordination tool for internal teams, providers, and client approvers.
 
 ## Primary Users
 
@@ -16,8 +16,12 @@ It is not a public social network. It is a workspace-based coordination tool for
 
 ## Core Product Shape
 
-- workspace-based account boundary
-- agencies able to manage multiple workspaces
+- organizations as the SaaS account, billing, subscription, and connector boundary
+- workspaces as brand/client workflow boundaries owned by one organization
+- agencies, in-house teams, and professional businesses able to manage multiple workspaces
+- organization members able to inherit access across owned workspaces
+- external collaborators able to access specific workspaces without organization membership
+- channels configured inside brand/client workspaces
 - content items as the main reviewable unit
 - assets and revisions tracked against content items
 - comments and approvals attached to the work itself
@@ -38,10 +42,11 @@ It is not a public social network. It is a workspace-based coordination tool for
 - full direct publishing engine
 - full DAM platform
 - analytics suite
-- billing or subscription flows
+- full billing provider integration and pricing/package automation
 
 ## Current Sources
 
 - `docs/product/vision.md`
 - `docs/product/glossary.md`
 - `docs/constraints.md`
+- `docs/FEATURES/organizations.md`