fix(data): replace deprecated GJ 702A with 1221-DXP9 in star registry

GJ 702A was a deprecated binary system entry. Replace with GJ 1221,
a real catalog star — DXP9 peculiar magnetic white dwarf at 20.03 ly.
Dead-end topology connecting to EZ Aqr (GJ 866A).

Updates: star-map.json, systems.db, gj-catalog-real.json, catalog.md,
EZ Aqr topology reference. New wiki entry and Drifter's Guide entry.
System count restored to 301.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/design/star-map.json

@@ -1870,7 +1870,7 @@
       "hop_distance_from_gateway": 8
     },
     {
-      "system_id": "GJ 702A",
+      "system_id": "GJ 1221",
       "gate_topology": "dead_end",
       "aperture_count": 1,
       "gate_connections": 1,
@@ -3240,7 +3240,7 @@
       "GJ 1156"
     ],
     [
-      "GJ 702A",
+      "GJ 1221",
       "GJ 866A"
     ],
     [
@@ -3464,4 +3464,4 @@
       "GJ 71"
     ]
   ]
-}
+}