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.

scripts/qa-failstate-b10.mjs

@@ -10,7 +10,7 @@
  * upstream failures so the run is deterministic and never depends on live
  * AISStream / CelesTrak availability:
  *
- *   (i)  AIS invalid key   — /api/ais-live is answered with
+ *   (i)  AIS invalid key   — /api/vessels is answered with
  *        {rows:[],status:'error',error:'invalid key'}. Assert the layer's
  *        getStats().error is set (feed down) — NOT a clean 'just now · 0'.
  *
@@ -193,7 +193,7 @@ async function main() {
     page.on('request', (req) => {
       const url = req.url();
       // (i) AIS invalid-key: the exact payload the spec calls for.
-      if (url.includes('/api/ais-live') && !url.includes('/track')) {
+      if (url.includes('/api/vessels') && !url.includes('/track')) {
         req.respond({
           status: 200,
           contentType: 'application/json',