data(content): rebalance 5 thin afrikaans systems to MENA heritage (#1019)

The corridor over-represented southern-African heritage (afrikaans on 15
systems; arab=2, persian/turkic=0) as an artifact of the earlier
name-balancing overcorrecting. Convert five genuinely-thin afrikaans
systems — whose distinctive threads are heritage-agnostic — into
Arab/Persian/Turkic founders so the cultural cascade is built on a
balanced set. Load-bearing mystery systems (Eerste Wacht / Helderoog /
Brandpunt etc.) are left untouched.

  Droëland  (GJ 914A)  -> Marib    (arab)
  Stilwater (GJ 508A)  -> Sawad    (arab)
  Koeberg   (GJ 1245B) -> Akhgar   (persian)
  Skuilplek (GJ 722)   -> Siginak  (turkic)
  Carnarvon (GJ 680)   -> Golestan (persian; Mostert dynasty -> Farahani)

Result: afrikaans 15->10; arab 0->2, persian 0->2, turkic 0->1.

Full narrative retouch (not just names): gttr.md + index.md prose,
body/station proper_names, cultural_specialization, gttr_hook,
atlas_city_names, and the four brand-corps named after the converted
systems (corp IDs kept stable; only display names + products renamed).
Cross-references in neighbour systems, the catalog, the aggregate
drifter guides, and the atlas proposals are updated to match.

arab/persian/turkic added to _CULTURAL_HERITAGE so the values validate;
the full canonical 47-value migration remains #1016.

Also fixes a pre-existing canon bug: Sawad (GJ 508A) no longer claims
GJ 914A is "unsettled" — it is Marib, a three-century settlement.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/atlas/proposals/GJ508A.json

@@ -1,6 +1,6 @@
 {
   "system_id": "GJ 508A",
-  "proper_name": "Stilwater",
+  "proper_name": "Sawad",
   "star_type": "M",
   "spectral_class": "M2V",
   "wiki_data": {
@@ -34,7 +34,7 @@
     },
     {
       "body_id": "GJ508Ac",
-      "proper_name": "Uithoek",
+      "proper_name": "Rusafa",
       "body_type": "planet",
       "orbit_index": 2,
       "parent_body_id": null,
@@ -50,7 +50,7 @@
       "economic_role": "agricultural",
       "settlement_pattern": "dispersed",
       "industrial_corridor": "agricultural_export",
-      "notes": "primary inhabited world; wave_4 Afrikaans heritage ('far corner'); 2-aperture through_route; M2V quiet star; unremarkable and deliberately so; plentiful land, infrequent neighbors; community council governance; Landbou Raad cooperative network (informal distribution agreements); Commission charter filing office (two-day medical station); agricultural consumption with modest surplus; Breëvlei visible as glow on clear nights"
+      "notes": "primary inhabited world; wave_4 Arab heritage ('far corner'); 2-aperture through_route; M2V quiet star; unremarkable and deliberately so; plentiful land, infrequent neighbors; community council governance; Landbou Raad cooperative network (informal distribution agreements); Commission charter filing office (two-day medical station); agricultural consumption with modest surplus; Breëvlei visible as glow on clear nights"
     },
     {
       "body_id": "GJ508A-belt",
@@ -176,7 +176,7 @@
   "stations": [
     {
       "station_id": "GJ508A-oort-S1",
-      "proper_name": "Stilwater Horizon",
+      "proper_name": "Sawad Horizon",
       "orbits_body_id": "GJ508A-oort",
       "station_type": "horizon",
       "population": 140,