feat(flights): show the tracked aircraft's Planespotters photo in Contacts

Tracking a civil flight asks Planespotters for that aircraft's photo, once
per aircraft, straight from the browser. The CONTEXT panel's CONTACTS view
shows it under the flight's name with the photographer's credit, as a plain
link to the photo's page. Only images on plnspttrs.net and pages on
www.planespotters.net are ever shown or linked. Military aircraft and a
converted TR-3B are never looked up.

Flight lookups (type, route, photo) whose source failed temporarily are
asked again after a 60-second cool-down; an answer, found or not, and a
permanent refusal stay final for the session. A route belongs to the
callsign it was looked up for, so a callsign change drops the old route.

Browser QA scripts that track a flight answer the photo lookup themselves,
so they never call the third party.

package.json

@@ -99,6 +99,7 @@
       "node": "./server/providers/live.js"
     },
     "./sources/adsb-lol": "./src/data/adsbLolFallback.js",
+    "./sources/planespotters": "./src/data/planespottersPhoto.js",
     "./server/providers/places": {
       "node": "./server/providers/places.js"
     },