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.

server/providers/aircraft/adsb-lol.js

@@ -1,7 +1,7 @@
 /**
  * Vite plugin: adsb.lol military aircraft proxy with 12 s response cache.
  *
- * Proxies GET /api/adsblol/mil to https://api.adsb.lol/v2/mil. When upstream
+ * Serves GET /api/military from https://api.adsb.lol/v2/mil. When upstream
  * fails — a thrown fetch OR a non-OK status such as 429 — the proxy serves its
  * cached body as STALE instead of relaying the failure, and it backs off from
  * upstream for the Retry-After period (bounded) so a rate limit is never
@@ -55,10 +55,11 @@ export function adsbLolProxy() {
     res.writeHead(status, {
       'Content-Type': 'application/json',
       'Cache-Control': 'no-store',
-      'X-ADS-B-Cache': cacheStatus,
+      'X-Feed-Source': 'adsb.lol',
+      'X-Feed-Cache': cacheStatus,
       ...(['HIT', 'STALE'].includes(cacheStatus)
         ? {
-            'X-ADS-B-Cache-Age-Ms': String(Math.max(0, Date.now() - _cacheAt)),
+            'X-Feed-Age-Ms': String(Math.max(0, Date.now() - _cacheAt)),
           }
         : {}),
       ...extra,
@@ -67,8 +68,11 @@ export function adsbLolProxy() {
   }
 
   const installMiddleware = (server) => {
-    server.middlewares.use('/api/adsblol/mil', async (req, res) => {
+    server.middlewares.use('/api/military', async (req, res, next) => {
       try {
+        // This mount also matches its /track route, served by its own handler.
+        if (new URL(req.url || '/', 'http://localhost').pathname !== '/')
+          return next();
         const now = Date.now();
         if (_cache && now - _cacheAt < CACHE_MS) {
           serve(res, 200, _cache, 'HIT');