infospace: process book-1-chapter-03

Extract entities, map to VSM, and synthesize analysis.

examples/infospace-with-history/output/entities/market-access-gradient.md

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+# Market Access Gradient
+
+## Definition
+
+The gradual decrease in market size and economic opportunity as distance from major trade routes, ports, or population centres increases. Market access gradients create patterns of economic development where coastal and riverine areas develop first and most fully.
+
+## Source Chapter
+
+Book I, Chapter 3
+
+## Context
+
+Smith's analysis shows how industry naturally begins on sea-coasts and along navigable rivers, and only later extends to inland parts of the country, creating a gradient of economic development based on market access.
+
+## Economic Domain
+
+Exchange
+
+---