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.

server/providers/local-receivers.js

@@ -27,13 +27,13 @@ import { normalizeDump1090Aircraft } from '../../src/sources/adsbRecords.js';
  */
 
 export const LOCAL_RECEIVERS_ROUTE = '/api/local-receivers/aircraft';
-export const LOCAL_RECEIVER_FEEDS_ENV = 'LOCAL_RECEIVER_FEEDS';
-export const LOCAL_RECEIVER_BANDS = Object.freeze(['1090', '978']);
-export const LOCAL_RECEIVER_TIMEOUT_MS = 2_000;
-export const LOCAL_RECEIVER_MAX_BODY_BYTES = 2 * 1024 * 1024;
-export const LOCAL_RECEIVER_CACHE_MS = 1_000;
+const LOCAL_RECEIVER_FEEDS_ENV = 'LOCAL_RECEIVER_FEEDS';
+const LOCAL_RECEIVER_BANDS = Object.freeze(['1090', '978']);
+const LOCAL_RECEIVER_TIMEOUT_MS = 2_000;
+const LOCAL_RECEIVER_MAX_BODY_BYTES = 2 * 1024 * 1024;
+const LOCAL_RECEIVER_CACHE_MS = 1_000;
 /** A feed whose own `now` is older than this is reported stale. */
-export const LOCAL_RECEIVER_STALE_MS = 10_000;
+const LOCAL_RECEIVER_STALE_MS = 10_000;
 const MAX_FEEDS = 8;
 const LOG_PREFIX = '[local-receivers]';
 
@@ -139,7 +139,7 @@ class FeedError extends Error {
  * @param {string} address Resolved IP address.
  * @returns {boolean}
  */
-export function isLocalReceiverAddress(address) {
+function isLocalReceiverAddress(address) {
   const value = String(address || '').toLowerCase();
   if (value === '::1') return true;
   const mapped = /^::ffff:(\d{1,3}(?:\.\d{1,3}){3})$/.exec(value);
@@ -152,7 +152,7 @@ export function isLocalReceiverAddress(address) {
  * @param {typeof dnsLookup} lookupImpl `dns.promises.lookup`-compatible.
  * @returns {Promise<Array<{address:string, family:number}>>}
  */
-export async function resolveLocalReceiverAddresses(hostname, lookupImpl) {
+async function resolveLocalReceiverAddresses(hostname, lookupImpl) {
   let resolved;
   try {
     resolved = await lookupImpl(hostname, { all: true, verbatim: true });
@@ -274,7 +274,7 @@ function fetchLocalReceiverFeed(url, options) {
  * @param {object} options
  * @returns {Promise<object>} Parsed JSON document.
  */
-export async function fetchLocalReceiverDocument(
+async function fetchLocalReceiverDocument(
   url,
   {
     fetchImpl = fetchLocalReceiverFeed,