Show Navara imagery at full detail and discard Esri's empty tiles

The tile budget left 768 MiB for tiles over the screen buffers, while an
oblique view needs about 0.9 GiB at 960x640 and 1.2 GiB at 1440x900; over
budget Navara coarsens the view and stops loading, so the start view stayed
at imagery level 15 where Cesium shows 17. The room for tiles is now
Navara's device default (a quarter of device memory, at most 2 GiB).

Terrain tiles also split past the keyless mesh's level 14, so imagery can
refine beyond level 15, and OSM stops at its level 19.

Esri answers a tile it has no imagery for with a grey "Map data not yet
available" image (over open ocean from level 14). Cesium discards it and
keeps the parent level; on Navara that tile now fails the same way.

scripts/package-boundaries.json

@@ -2880,7 +2880,8 @@
       "src/ui/kit/UiSelect.js",
       "src/ui/news/NewsCard.vue",
       "src/ui/news/NewsFeed.vue",
-      "src/ui/newsPanel.js"
+      "src/ui/newsPanel.js",
+      "src/globe/navara/missingTiles.js"
     ],
     "external": [
       "hls.js",