fix(gnss): expire stale cells on re-enable; pin the unpruned return-after-window path

Re-enabling after a disable longer than the window no longer shows the
old cells until the next refresh. A healthy report arriving 31 minutes
after a degraded one, with no prune in between, starts clean; exactly
30 minutes still counts.

src/layers/gnss/index.js

@@ -122,7 +122,11 @@ export function createGnssIntegrityLayer({
 
     enable() {
       _enabled = true;
-      if (_dataSource) _dataSource.show = true;
+      // Cells left from before a long disable must not reappear past the window.
+      if (_dataSource) {
+        expire();
+        _dataSource.show = true;
+      }
     },
 
     disable() {