refactor(street-level): trim dead paths, duplicated labels and test-only API

- visibleBbox: no view-rectangle fallback or grid option; its one caller
  always ranges the rays
- tilesForBbox returns the tiles; normalizeBbox takes arrays only
- viewerHost: no try/catch around adapter calls that catch for themselves
- coverage: counts come from the drawn sequences; no sequenceCount export
- one keyStatusLabel for the pill and the layer list
- no constructor source check, double-init guard or selectSequence /
  clearSequence on the layer

Co-Authored-By: Claude Opus 5.5 <[email protected]>

scripts/package-boundaries.json

@@ -660,6 +660,7 @@
       "src/ui/shellFacade.js",
       "src/ui/streetLevelControls.js",
       "src/ui/streetLevelPresentation.js",
+      "src/layers/streetLevel/policy.js",
       "src/ui/localSdrControls.js",
       "src/layers/localAdsb/feedNames.js",
       "src/ui/localSdrPresentation.js",