feat: refine ISAC media and notification workflows

docs/architecture.md

@@ -367,6 +367,19 @@ time by the static `/missing-item-icon.svg` asset through the shared
 `MISSING_ITEM_ICON_URL` constant and `ItemIcon` component. The placeholder does
 not enter `game_data_icons`. A later edit or proposal can attach the real icon
 without recreating the canonical item.
+
+`source_entity_type` and `source_entity_id` link each `game_data_icons` row to a
+`managed_images` record. Both records share one storage key and one WebP file.
+The managed record adds the searchable library name, category, tags, creator,
+dimensions, and assignment state. Game-data icon saves upsert this record, keep
+operator-edited metadata, and merge current entity-context tags. Removing a
+source icon removes the linked library record and shared file.
+
+The additive database migration registers older game-data icons and selects an
+administrator or the earliest active account as the migration actor. ISAC and
+managed-image exports accept linked storage keys. Environment synchronization
+keeps the library metadata and one copy of each file.
+
 # Oversight notification dispatch
 
 New Data Change and Avatar Oversight review items are routed only to agents who