feat(schema): D-237 specialization columns + specialization_vocabulary table

Ticket #1011. system_economy gains economic_specialization +
cultural_specialization (TEXT, NULL = heuristic fallback); new
specialization_vocabulary table (specialization_id PK, commodity_id
FK->commodities, production_ubiquity_override, projected BulkClass +
ProductionUbiquity for D-233, description) + commodity index. Columns
mirrored into COLUMN_MIGRATIONS for idempotent migration; table rides
systems-schema.sql. dominant_faction already exists on system_factions
(populate-only). Validated: importer parses; schema applies to scratch DB;
idempotent migration ran 2x on a copy of live systems.db, 301 rows preserved.

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

tooling/economy-db/import_economics.py

@@ -417,6 +417,8 @@ COLUMN_MIGRATIONS = [
     ("bodies", "body_radius_km", "REAL"),  # D-204 — physical radius in km, nullable
     ("meta", "schema_sha", "TEXT"),
     ("atlas_city_names", "settlement_class", "TEXT"),  # D-196 — NULL until placement (#37)
+    ("system_economy", "economic_specialization", "TEXT"),  # D-237 — authored specialization layer
+    ("system_economy", "cultural_specialization", "TEXT"),  # D-237 — authored specialization layer
 ]