reinsertShellForNativeBindIfNeeded

Re-inserts a shell Tile when nativeCache/GPU still has pixels for hash (per hasBindableEncodedPixels) but the entry is missing from tiles/_persistents — e.g. the LRU evicted it — so bindTextures can restore EncodedData.paddedData without another HTTP request. Returns true if the tile is bindable (whether or not a shell needed inserting).