Simplify Section 3 title to "The Knowledge Graph"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Boris Dev

docs/domain-grammar-compiler.md

@@ -142,7 +142,7 @@ The lexicon sits outside the IR but inside the I-Language. It maps surface forms
 
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-## 3. The Knowledge Graph Is a Compiled Program
+## 3. The Knowledge Graph
 
 The knowledge graph is not the IR. It is the **compiled output** — the execution-ready representation built from validated IR instances.