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.

docs/opensky-auth.md

@@ -1,6 +1,6 @@
 # OpenSky Auth Setup
 
-God's Eye View uses explicit auth modes for `/api/opensky`:
+God's Eye View uses explicit auth modes for `/api/flights`:
 
 - `OPENSKY_AUTH_MODE=oauth` (default, recommended)
 - `OPENSKY_AUTH_MODE=auto` (OAuth first, then Basic fallback)
@@ -54,7 +54,7 @@ OPENSKY_AUTH_MODE=basic ./scripts/dev-fresh.sh
 Inspect proxy headers:
 
 ```bash
-curl -si http://localhost:4173/api/opensky | grep -iE 'HTTP/|X-OpenSky-Auth'
+curl -si http://localhost:4173/api/flights | grep -iE 'HTTP/|X-OpenSky-Auth'
 ```
 
 Useful reasons: