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>

tooling/wiki/gj-catalog-real.json

@@ -1,7 +1,7 @@
 {
   "source": "HYG Database v4.1 (astronexus/HYG-Database)",
   "selection": "215 nearest G/K/F + 75 nearest M + 10 nearest unusual GJ stars",
-  "count": 300,
+  "count": 301,
   "distance_range_ly": [
     4.2,
     46.8
@@ -2706,6 +2706,14 @@
       "spect": "K5V",
       "mag": "8.56",
       "absmag": "7.776"
+    },
+    {
+      "gj_id": "GJ 1221",
+      "common_name": "DXP9",
+      "distance_ly": 20.03,
+      "spectral_type": "DXP9",
+      "ra": "17.804188",
+      "dec": "70.874972"
     }
   ]
 }