fix: report stale transit feeds and drop expired positions

get_transit_vehicles returned positions from a feed the proxy served from
its error cache, and hour-old fixes, as current. It now applies the transit
layer's rules: a feed is stale when the proxy says so or the operator has
not answered recently, and fixes older than the vehicle limit are dropped
and counted.

scripts/package-boundaries.json

@@ -3123,7 +3123,11 @@
       "src/tools/queries/events.js",
       "src/data/bhoteKoshiFloodPath.js",
       "src/tools/functions.js",
-      "src/tools/surfaces.js"
+      "src/tools/surfaces.js",
+      "src/layers/transit/policy.js",
+      "src/data/transitFeeds.js",
+      "src/layers/transit/movement.js",
+      "src/data/contactPlayback.js"
     ],
     "external": ["satellite.js"]
   },