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/sources/adsbRecords.js

@@ -41,12 +41,12 @@ const CATEGORY_PATTERN = /^[A-D][0-7]$/;
 /** A previous accepted fix older than this is no reference for a new one. */
 export const LOCAL_ADSB_REFERENCE_MAX_AGE_MS = 10 * 60_000;
 /** Speed limit (kt) for an aircraft that has not reported a ground speed. */
-export const LOCAL_ADSB_UNKNOWN_SPEED_LIMIT_KT = 1_000;
+const LOCAL_ADSB_UNKNOWN_SPEED_LIMIT_KT = 1_000;
 /** Tighter limit (kt) for light aircraft and rotorcraft without a speed. */
-export const LOCAL_ADSB_SLOW_CATEGORY_LIMIT_KT = 350;
+const LOCAL_ADSB_SLOW_CATEGORY_LIMIT_KT = 350;
 /** Reported ground speed is multiplied by this, plus the margin below. */
-export const LOCAL_ADSB_SPEED_FACTOR = 1.5;
-export const LOCAL_ADSB_SPEED_MARGIN_KT = 50;
+const LOCAL_ADSB_SPEED_FACTOR = 1.5;
+const LOCAL_ADSB_SPEED_MARGIN_KT = 50;
 /** Distance always allowed between two fixes (CPR and reception error). */
 export const LOCAL_ADSB_POSITION_MARGIN_M = 500;
 /**