docs(sprints): mark Track D (West Reach) done in copy briefing

Also includes star_type DB fixes and proposal file updates from
the west_reach authoring session.

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

docs/atlas/proposals/GJ208.json

@@ -39,7 +39,7 @@
       "orbit_index": 2,
       "parent_body_id": null,
       "inhabited": true,
-      "population": 42000,
+      "population": 800,
       "mass_class": "terrestrial",
       "surface_gravity": 0.84,
       "orbital_period_days": 100.0,

docs/atlas/proposals/GJ231.json

@@ -144,7 +144,7 @@
       "surface_gravity": 0.13,
       "orbital_period_days": 6.4,
       "rotation_period_hours": 153.6,
-      "atmosphere": "trace",
+      "atmosphere": null,
       "biome_summary": "frozen",
       "hydrosphere": null,
       "economic_role": null,

docs/atlas/proposals/GJ320.json

@@ -124,7 +124,7 @@
       "surface_gravity": 0.12,
       "orbital_period_days": 5.6,
       "rotation_period_hours": 134.4,
-      "atmosphere": "trace",
+      "atmosphere": null,
       "biome_summary": "frozen",
       "hydrosphere": null,
       "economic_role": null,

docs/atlas/proposals/GJ453.json

@@ -124,7 +124,7 @@
       "surface_gravity": 0.12,
       "orbital_period_days": 5.6,
       "rotation_period_hours": 134.4,
-      "atmosphere": "trace",
+      "atmosphere": null,
       "biome_summary": "frozen",
       "hydrosphere": null,
       "economic_role": null,