feat: add managed ISAC image library

docs/DESIGN_SYSTEM.md

@@ -1564,6 +1564,31 @@ navigation regions. Search fields have visible or accessible labels, keyboard
 focus uses Signal Orange, and collapsed state must remain understandable
 without motion.
 
+### Managed image library
+
+Reusable uploaded visuals belong in the ISAC Image Library under System
+Configuration. Present assets as a dense responsive registry of preview cards:
+the artwork is primary, while name, assignment category, tags, dimensions, and
+file size remain compact operational metadata. A checkerboard preview surface
+may make transparency legible without changing the asset.
+
+Image intake uses the shared picker, drop-zone, and clipboard control. The
+`Normalize as icon` option trims transparent outer margins and standardizes the
+canvas. When the source has no usable transparency, the server requests
+preview-resolution background removal before local normalization and reports
+configuration, credit, rate-limit, foreground-detection, or network failures
+with a specific recovery. Its dependent `Force white` option converts visible pixels to the
+canonical neutral icon color while preserving alpha. Both controls state their
+processing consequence in text, expose checked and disabled states, and remain
+keyboard accessible. Metadata edits preserve the stable asset identity, close
+after a successful save, and use the shared toast and editor lifecycle.
+
+Use controlled assignment categories for broad placement and free-form,
+normalized tags for discovery. Names are unique and human-readable. Search
+covers names, categories, and tags. On narrow screens, processing controls
+stack vertically and cards reduce to one column so previews and actions retain
+usable sizes.
+
 ### ISAC mutation consequence
 
 Every writable game-data module states what Save will do before the operator