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/vessels/ais-live.js

@@ -71,14 +71,15 @@ let _aisWebSocketImpl;
  */
 export function aisLiveProxy() {
   function install(middlewares) {
-    middlewares.use('/api/ais-live', async (req, res) => {
+    middlewares.use('/api/vessels', async (req, res) => {
       try {
+        res.setHeader('X-Feed-Source', 'AISStream');
         ensureAisStreamConnection();
         const incoming = new URL(req.url || '', 'http://localhost');
 
         // Track sub-route MUST be handled before the rows snapshot — this
         // mount prefix-matches every subpath, so without this branch
-        // /api/ais-live/track would be silently answered with vessel rows.
+        // /api/vessels/track would be silently answered with vessel rows.
         if (
           incoming.pathname === '/track' ||
           incoming.pathname.startsWith('/track/')
@@ -288,7 +289,7 @@ function aisKeyFingerprint() {
 }
 
 /**
- * Drive the watchdog once. Called on every /api/ais-live request and on the
+ * Drive the watchdog once. Called on every /api/vessels request and on the
  * background interval, so recovery does not depend on browser traffic.
  */
 function ensureAisStreamConnection() {
@@ -307,7 +308,7 @@ function ensureAisStreamConnection() {
     keyFingerprint: aisKeyFingerprint(),
   });
 }
-/** Status metadata for /api/ais-live, safe to call before the first connect. */
+/** Status metadata for /api/vessels, safe to call before the first connect. */
 function aisStreamStatusSnapshot() {
   const snapshot = _aisAdapter ? _aisAdapter.snapshot() : null;
   if (snapshot) return snapshot;