content: add ui/designs/ collection (ecomm#8)

Standard third content-repo collection alongside specs/ and plans/: UI-design
artifacts (Claude Design outputs generated from a Solution Design), referenced
from specs. Spec-linkage gate + backfill gesture tracked in
wiggleverse-dev-claude-plugin#93.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -11,6 +11,7 @@ repo.
 | --- | --- |
 | `specs/` | reviewed Solution-Design specs (submitted at session finalize) |
 | `plans/` | archived implementation plans |
+| `ui/designs/` | UI-design artifacts (Claude Design outputs), referenced from specs |
 
 Roadmap and the deployment version `pin` will be added as the build gets underway.
 

ui/designs/README.md

@@ -0,0 +1,13 @@
+# ui/designs — UI-design artifacts
+
+Standard content-repo collection (alongside `specs/` and `plans/`) holding this
+app's UI-design artifacts — primarily Claude Design outputs generated from a
+Solution Design (rubric: `engineering/solution-design/claude-design-vs-code.md`).
+
+A Solution Design with a UX-involving slice references its design artifact here
+by path. The spec-linkage gate and the backfill gesture for adding that
+reference once a design exists are tracked in
+[wiggleverse-dev-claude-plugin#93](https://git.wiggleverse.org/wiggleverse/wiggleverse-dev-claude-plugin/issues/93).
+
+Suggested layout: one subfolder per design, named for the spec/slice it serves,
+e.g. `ui/designs/SD-0001-slice-3-storefront/`.