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/sdr/controller.js

@@ -38,12 +38,12 @@ const READ_PIPELINE_DEPTH = 4;
 const RATE_WINDOW_MS = 1_000;
 // A bulk read that has not completed in this long is treated as a stalled
 // USB transfer: the session is torn down instead of waiting forever.
-export const SDR_READ_STALL_MS = 5_000;
+const SDR_READ_STALL_MS = 5_000;
 // Decoder admission. Every block sent to the worker is numbered and must be
 // acknowledged; past these bounds the receiver stops with an overload error
 // rather than queueing raw IQ the decoder cannot keep up with. Eight 16 ms
 // blocks is 128 ms of input, about forty times the measured decode cost.
-export const SDR_WORKER_ADMISSION = Object.freeze({
+const SDR_WORKER_ADMISSION = Object.freeze({
   maxBlocks: 8,
   maxBytes: 8 * 65_536,
   maxAgeMs: 1_000,
@@ -66,7 +66,7 @@ const DECODER_WINDOW_SAMPLES = 256;
 // raw USB device is closed directly, which aborts any pending transfer. The
 // raw close is bounded by the same deadline, so a teardown settles within
 // twice this even when `USBDevice.close()` itself never settles.
-export const SDR_CLOSE_TIMEOUT_MS = 2_000;
+const SDR_CLOSE_TIMEOUT_MS = 2_000;
 
 /** Tuning presets per receiver mode; gain is a separate per-mode setting. */
 export const SDR_RECEIVER_PRESETS = Object.freeze({
@@ -1912,9 +1912,3 @@ function formatMhz(hz) {
 function positiveModulo(value, divisor) {
   return ((value % divisor) + divisor) % divisor;
 }
-
-export const SDR_FM_BAND = Object.freeze({
-  minHz: FM_MIN_HZ,
-  maxHz: FM_MAX_HZ,
-});
-export const SDR_ADSB_FREQUENCY_HZ = ADSB_FREQUENCY_HZ;