v0.68.0: re-curate special remote airports — one per ~1000 km region (ISS-144)

Greedy sparse selection replaces the blanket 1000km-from-large filter that
over-filled central Australia / Canada edges with dozens of tiny strips:
candidates sorted by scheduled service, type rank (medium < small < seaplane),
numeric id; accepted only if >= REMOTE_RADIUS_KM from every already-accepted
special. CSV: 1483 -> 1161 rows (1119 large unchanged, specials 364 -> 42).
New unit test pins the pairwise-sparsity invariant on the committed dataset.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "flight-ops",
-  "version": "0.67.0",
+  "version": "0.68.0",
   "private": true,
   "scripts": {
     "dev": "next dev -p 3000",