chore: drop exports nothing imports

Knip, configured with the application, package exports, scripts, QA
harnesses, workers, tools and tests as entry points, reports exports
that no module imports. Each was checked by hand against string-based
and namespace imports.

- Symbols that are still used inside their own module lose only the
  `export` keyword (176 constants and helpers).
- Unused re-exports are removed from barrel modules (flight, military,
  vessel, CCTV, directions, transit history, local ADS-B and street-level
  policy modules).
- Declarations that nothing uses at all are deleted, among them
  AIS_WATCHDOG_STATUSES, applyFilter, isRadioCountryCode, compactText,
  DENSITY_STOPS, the unused CCTV endpoint constants, and the SDR band
  constants.
- Default exports that nothing imports are removed. The ones in
  src/data/earthquakes.js, src/data/telegeographySubmarineCables.js,
  src/data/wind.js and src/data/bhoteKoshiLocator.js each constructed a
  layer instance at import time that nothing used; those instances are
  no longer created.

Every export of a package.json entry stays, as does TOMTOM_CREDIT,
which the traffic layer reads from the credits namespace it is given.

src/sky/stars.js

@@ -18,7 +18,7 @@ export const STAR_MAX_SIGMA_PX = 1.35;
 /** Peak opacity of the faintest star. */
 export const STAR_MIN_ALPHA = 0.22;
 /** B−V for stars the catalogue gives no colour (a solar-type white). */
-export const STAR_DEFAULT_BV = 0.6;
+const STAR_DEFAULT_BV = 0.6;
 /** Floats per star in the vertex buffer: xyz, σ, rgb, alpha. */
 export const STAR_VERTEX_FLOATS = 8;
 
@@ -76,7 +76,7 @@ export function bvToTemperature(bv) {
 }
 
 /** Black-body colour of a temperature, sRGB 0..1 (Helland's fit). */
-export function temperatureToRgb(kelvin) {
+function temperatureToRgb(kelvin) {
   const t = clamp(kelvin, 1000, 40000) / 100;
   const red = t <= 66 ? 255 : 329.698727446 * (t - 60) ** -0.1332047592;
   const green =