feat: name live feed routes and sources for what they serve

The flight, military and vessel feeds were named after the providers the
bundled server uses (/api/opensky, /api/adsblol/mil, /api/ais-live and
their track routes; createOpenSkySource, createAdsbLolSource,
createAisStreamSource). Any server should be able to answer a feed from
its own provider, so the feeds are now:

  /api/flights   /api/flights/track?icao24=
  /api/military  /api/military/track?hex=
  /api/vessels   /api/vessels/track?mmsi=

with createFlightSource, createMilitarySource and createVesselSource. The
old routes are removed. Each server names its provider in X-Feed-Source
(the bundled server sends OpenSky Network, adsb.lol and AISStream, so its
attribution is unchanged) and the military feed's cache state and age in
X-Feed-Cache and X-Feed-Age-Ms. Sources report the provider the server
names and fall back to the feed's name.

src/data/flights.js

@@ -1,12 +1,12 @@
 import { defaultSurface } from './surfaceServices.js';
 import { createApplicationFlights } from '../app/layers/flights.js';
 
-import { createOpenSkySource } from '../sources/live/standalone.js';
+import { createFlightSource } from '../sources/live/standalone.js';
 import * as militaryRegistry from './militaryRegistry.js';
 
 const flightsLayer = createApplicationFlights({
   surface: defaultSurface,
-  source: createOpenSkySource(),
+  source: createFlightSource(),
   militaryRegistry,
 });
 export { TRACKED_MODEL_MAX_PX } from '../layers/flights/policy.js';