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/layers/transit/policy.js

@@ -99,7 +99,7 @@ export const VISIBILITY_REFRESH_MS = 250;
  * on screen. Generous on purpose: a vehicle that crosses the edge mid-glide
  * should already have been moving, not pop into motion at the border.
  */
-export const VIEW_MARGIN_RATIO = 0.6;
+const VIEW_MARGIN_RATIO = 0.6;
 
 /**
  * Whether a vehicle is close enough to the camera's look-at area to be worth
@@ -516,10 +516,10 @@ export function createTransitSelectedOverlayEntry(key, position, copy, mode) {
 }
 
 /** Modes that ordinarily run below the street, drawn on the surface above themselves. */
-export const UNDERGROUND_MODES = new Set(['subway']);
+const UNDERGROUND_MODES = new Set(['subway']);
 
 /** The mode in plain words, for a card a person reads rather than scans. */
-export const TRANSIT_MODE_WORD = Object.freeze({
+const TRANSIT_MODE_WORD = Object.freeze({
   bus: msg('Bus'),
   tram: msg('Tram'),
   subway: msg('Subway'),
@@ -529,7 +529,7 @@ export const TRANSIT_MODE_WORD = Object.freeze({
 });
 
 /** Short, fixed-width mode word for the detection card's class field. */
-export const TRANSIT_MODE_ABBR = Object.freeze({
+const TRANSIT_MODE_ABBR = Object.freeze({
   bus: 'BUS',
   tram: 'TRAM',
   subway: 'METRO',
@@ -588,7 +588,7 @@ export function transitDetectionId(record, feed = null) {
 }
 
 /** Longest route text the single-line detection label can carry. */
-export const DETECTION_ID_MAX_CHARS = 14;
+const DETECTION_ID_MAX_CHARS = 14;
 
 /**
  * Cut long route text with an ellipsis, so a reader can see it was cut.
@@ -600,7 +600,7 @@ export const DETECTION_ID_MAX_CHARS = 14;
  * @param {string} text
  * @returns {string} Uppercase, at most DETECTION_ID_MAX_CHARS characters.
  */
-export function elideRouteText(text) {
+function elideRouteText(text) {
   const value = String(text || '').toUpperCase();
   if (value.length <= DETECTION_ID_MAX_CHARS) return value;
   return `${value.slice(0, DETECTION_ID_MAX_CHARS - 1)}\u2026`;
@@ -659,6 +659,6 @@ export function transitDetectionMetric(
  * @param {number} [nowMs]
  * @returns {string}
  */
-export function transitVehicleState(entry, nowMs = Date.now()) {
+function transitVehicleState(entry, nowMs = Date.now()) {
   return displayMotion(entry, nowMs).word;
 }