chore: sync GovOPlaN module split state

docs/UNIFIED_INBOX_CONCEPT.md

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+# Unified Inbox Concept
+
+GovOPlaN should converge messages, tasks, notifications, postbox items, and
+workflow exceptions into a unified inbox without making one module own every
+item type.
+
+## Purpose
+
+Users should have one place to see work requiring attention:
+
+- assigned tasks
+- workflow manual exceptions
+- postbox messages
+- notifications
+- approvals
+- failed automation requiring review
+- appointment or booking decisions
+
+Each item remains owned by its domain module. The inbox is an aggregation and
+action surface.
+
+## Contract
+
+Inbox contributors should provide:
+
+- item id and owning module
+- actor/tenant visibility rules
+- title, summary, priority, due date, and status
+- required action and available commands
+- source object references
+- audit/provenance links
+- dismissal, completion, or deferral semantics
+
+The inbox must use core-mediated capabilities and DTOs. It should not import
+postbox, workflow, notification, or approval internals.