feat(schema): add gate_links and economics tables to systems-schema.sql (#813)

Extends systems.db schema with gate_links, commodities, production_chains,
chain_inputs, corp_presence, and currency_zones tables required for the
Phase 2 economics layer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/data/systems-schema.sql

@@ -41,6 +41,11 @@ CREATE TABLE IF NOT EXISTS star_systems (
     -- Economics (D-172)
     currency_zone TEXT DEFAULT 'TRACTUS_PRIMARY',  -- TRACTUS_PRIMARY | MARK_PRIMARY | MIXED
 
+    -- Energy-over-gate (D-186)
+    -- Gate Corp energy service: on-grid nodes get ~0.3× fusion_fuel utility demand.
+    -- MARK_PRIMARY zones default false (Compact refused Gate Corp dependency).
+    gate_energy_connected INTEGER DEFAULT 1,  -- boolean 0/1
+
     updated_at TEXT DEFAULT (datetime('now'))
 );