chore(db): backfill founding_age_years for inhabited bodies (#1000)

Add idempotent MIGRATION_SQL UPDATE to import_economics.py deriving
bodies.founding_age_years via COALESCE(colonial_charter event age,
settlement_wave fallback) per the D-216 amendment.

- Events-first: colonial_charter age_years (authored; 11 bodies).
- Wave fallback: wave_1=600/wave_2=500/wave_3=300/wave_4=100/wave_5=40
  (258 bodies).
- Exclude settlement_wave in (origin, unsettled) -> stays NULL: 4 Sol
  bodies remain NULL (out of player scope, D-236).

Source-canonical via regen-db; 269/273 inhabited bodies now populated.

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

tooling/economy-db/import_economics.py

@@ -358,6 +358,50 @@ UPDATE bodies SET economic_role = 'extraction'    WHERE economic_role IN ('minin
 UPDATE bodies SET economic_role = 'transit_hub'   WHERE economic_role = 'transit';
 UPDATE bodies SET economic_role = 'service_mixed' WHERE economic_role IN ('commercial', 'coordination');
 UPDATE bodies SET economic_role = 'residential'   WHERE economic_role = 'frontier';
+
+-- Backfill bodies.founding_age_years for all inhabited bodies in player scope (D-216 amendment,
+-- ticket #1000).  Idempotent: WHERE clause limits to NULL rows, so a re-run is a no-op.
+--
+-- Strategy: COALESCE(events-first, wave-fallback)
+--   events-first:  the system's colonial_charter event age_years (authored; 9 systems in live DB).
+--                  system_history is keyed PRIMARY KEY on system_id, so the wave subquery returns
+--                  at most one row; LIMIT 1 is used on historical_events for safety (max one
+--                  colonial_charter per system in the data).
+--   wave-fallback: canonical founding-edge of each settlement_wave range per D-216:
+--                  wave_1=600, wave_2=500, wave_3=300, wave_4=100, wave_5=40.
+--
+-- Exclusions (founding_age_years stays NULL):
+--   origin    — Sol; out of player scope per D-236.
+--   unsettled — 24 systems with inhabited=0; the EXISTS guard also excludes them.
+UPDATE bodies
+SET founding_age_years = COALESCE(
+    (
+        SELECT he.age_years
+        FROM historical_events he
+        WHERE he.system_id = bodies.system_id
+          AND he.event_type = 'colonial_charter'
+        LIMIT 1
+    ),
+    (
+        SELECT CASE sh.settlement_wave
+            WHEN 'wave_1' THEN 600
+            WHEN 'wave_2' THEN 500
+            WHEN 'wave_3' THEN 300
+            WHEN 'wave_4' THEN 100
+            WHEN 'wave_5' THEN 40
+        END
+        FROM system_history sh
+        WHERE sh.system_id = bodies.system_id
+    )
+)
+WHERE founding_age_years IS NULL
+  AND inhabited = 1
+  AND EXISTS (
+      SELECT 1
+      FROM system_history sh2
+      WHERE sh2.system_id = bodies.system_id
+        AND sh2.settlement_wave NOT IN ('origin', 'unsettled')
+  );
 """
 
 # Columns to add to existing tables (ALTER TABLE is idempotent via try/except)