docs: remove internal visibility rationale record from documentation

Author: ColinDaglish

docs/README.md

@@ -8,7 +8,6 @@ Keep docs short and practical.
 - `docs/how-to/`: task steps
 - `docs/reference/`: facts, inputs, outputs
 - `docs/explanation/`: rationale and trade-offs
-- `docs/PIRR.md`: internal visibility rationale record
 
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