refactor(ui): remove the map stack chip DOM builders

The dock renders the chips from the map source controls' published view,
so renderMapStackChips, syncMapStackChips and MAP_STACK_CHIP_CLASS have no
callers. Their tests now pin the chip models; the dock test keeps the
rendered chips' button type and native enablement.

docs/CODE-BOUNDARIES.md

@@ -399,9 +399,9 @@ remain in their callers.
 `ui/maps` owns source-chip presentation, selection feedback and its subscription
 lifetime. It receives the existing controller and explicit state/action callbacks;
 it imports no renderer or application. Source construction and availability policy
-remain with the map controller. Rebuilding controls removes their previous chip
-listeners, and destruction suppresses late completions without owning or destroying
-the supplied controller.
+remain with the map controller. The dock renders the chips; rebuilding controls
+drops their previous subscription, and destruction suppresses late completions
+without owning or destroying the supplied controller.
 
 ## Layer panel