chore: sync GovOPlaN module split state

docs/NOTIFICATION_INBOX_BOUNDARY.md

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+# Notification And Inbox Boundary
+
+`govoplan-notifications` should own delivery and notification state, but it
+should not become the owner of tasks, postbox messages, workflow exceptions, or
+approval records.
+
+Notifications can contribute lightweight inbox items when they require attention
+or acknowledgement. Domain modules remain responsible for the underlying
+business object and action commands.
+
+## Responsibilities
+
+Notifications owns:
+
+- notification channels and delivery preferences
+- notification templates and rendered delivery records
+- acknowledgement or dismissal state for notification-owned items
+- delivery attempts, failures, and audit events
+
+Notifications does not own:
+
+- task completion
+- postbox message read/write state
+- workflow transition decisions
+- approval semantics
+- case or record ownership
+
+The unified inbox should aggregate notification contributions through DTOs and
+capabilities shared with tasks, postbox, workflow, and portal.