Add persisted and shareable builds

docs/DESIGN_SYSTEM.md

@@ -1155,3 +1155,19 @@ back to a short orange text mark rather than removing the relationship.
 Use this pattern only for small bounded sets that remain scannable, such as the
 two-to-four compatible Brand Sets on Gear. Long or unbounded relationships
 continue to use counts, searchable inspection, or expanded detail views.
+
+### Build persistence and sharing
+
+The builder distinguishes device persistence from account persistence. `SAVE
+LOCALLY` writes a working draft to the current browser. Signed-in agents also
+receive one account-save action paired with an explicit visibility selector:
+
+- `PRIVATE` is owner-only.
+- `UNLISTED` is accessible by direct link but excluded from discovery.
+- `PUBLIC` is accessible by direct link and included in the public archive.
+
+Keep visibility adjacent to the account-save action and explain its selected
+state in plain language. Show a share-page action only after a non-private
+build has been saved. Public and unlisted build pages are read-only tactical
+summaries; owner editing returns to the builder. On narrow layouts,
+persistence controls and shared-loadout columns stack vertically.