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/tools/queries/aviation.test.mjs

@@ -373,10 +373,10 @@ test('aircraft searches say when a feed that answered is stale', async () => {
 });
 
 test('the real OpenSky source marks an hour-old snapshot stale for searches', async () => {
-  const { createOpenSkySource } =
+  const { createFlightSource } =
     await import('../../sources/live/standalone.js');
   const now = Date.UTC(2026, 0, 1, 12);
-  const opensky = createOpenSkySource({
+  const opensky = createFlightSource({
     now: () => now,
     fetchImpl: async () =>
       Response.json({ time: now / 1000 - 3600, states: [] }),