split data in separate files

docs/systems/trade-routes.md

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+# Trade Routes
+
+**Entity Type:** SystemEntity
+
+## Description
+
+Automated ship loop moving goods between islands.
+
+## Configuration
+
+1. Select ship
+2. Enable Trade Route
+3. Assign goods per cargo slot
+4. Assign islands for load/unload
+
+## Rules
+
+- Route loops indefinitely
+- Used to supply production chains across islands
+
+## Usage Patterns
+
+Specialize islands (agricultural vs industrial) and route goods accordingly.
+
+## Common Pitfalls
+
+Under-shipping (not enough cargo throughput) leads to need flicker and income oscillation.