feat(isac): support deferred item icons

docs/DESIGN_SYSTEM.md

@@ -1222,3 +1222,19 @@ Use explicit textual tier capacity wherever Gear tier is summarized: `1 MOD
 SLOT` for T0 and `2 MOD SLOTS` for T1/T2. On narrow screens the identity band
 and preview controls stack, while repeated quality data may scroll rather than
 compressing numeric controls below usable sizes.
+
+### Deferred game-data icons
+
+Game-data icons are optional enrichment, never a blocker for creating or
+proposing a canonical item. Upload fields must state that an icon may be
+contributed later and show the shared `/missing-item-icon.svg` artwork when no
+upload exists. Registries, relationship rails, and builder selection controls
+use the same placeholder instead of initials, empty boxes, or ad hoc glyphs.
+
+Treat the placeholder as an explicit incomplete-data state: keep its subdued
+SHD styling and useful alternative text where the surrounding item name is not
+already available. Do not persist placeholder metadata or copy the placeholder
+into per-item storage. A later contributor replaces it through the normal icon
+upload proposal, preserving the canonical record and audit history. The upload
+itself retains all transparent-format, size, SVG-safety, focus, drag/drop, and
+paste validation requirements.

docs/architecture.md

@@ -313,3 +313,11 @@ served by the validated `/icons/game-data/[type]/[id]` endpoint with immutable
 cache headers and MIME sniffing disabled. ISAC save actions process files
 before mutation, apply upload or removal after record validation, and include
 only safe icon metadata—not image bytes—in their audit snapshots.
+
+Icon metadata is optional. Canonical records and contributor proposals may be
+created without an upload, allowing values and artwork to be contributed in
+separate dependency-safe changes. Missing artwork is represented at render
+time by the static `/missing-item-icon.svg` asset through the shared
+`ItemIcon` component; the placeholder is never inserted into
+`game_data_icons`. A later edit or proposal can attach the real icon without
+recreating or replacing the canonical item.