fix(ui): the "kept in the link" notice is readable on Navara

On Navara the engine's persistent notice came up right after the share
restore's NOT ON THIS ENGINE notice and replaced it at once, so the names
of the linked layers this engine lacks were never seen (and a later finite
notice would in turn have wiped the engine notice for good).

- ShellFeedback keeps a persistent notice that a finite one covers and
  brings it back when the finite one ends; a persistent notice that arrives
  under a live finite one waits for it.
- Notices take a dwellMs; "Kept in the link: …" stays 15 s.
- scripts/qa-engine-notice.mjs (headless): a Cesium share link with a layer
  Navara lacks, opened with ?engine=navara: notice shown with the layer
  name, still up 14 s later, then the engine notice is back. 4/4 (before
  the fix the notice never appeared).

T8-T9 review item 2.

scripts/format-scope.json

@@ -1109,5 +1109,6 @@
   "src/app/layers/qaSources.test.mjs",
   "scripts/qa-w1-layers.mjs",
   "src/bench/w1Feeds.js",
-  "scripts/qa-map-switch.mjs"
+  "scripts/qa-map-switch.mjs",
+  "scripts/qa-engine-notice.mjs"
 ]