docs: align internal docs to enterprise standards

Add canonical operations/security/access/feature docs and fix path integrity to improve onboarding and incident readiness.

docs/features/README.md

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+# Major Feature Inventory
+
+This index tracks CBDDC major functionality. Each feature has one canonical document.
+
+## Features
+
+- [Selective Collection Sync](selective-collection-sync.md)
+- [Peer-to-Peer Gossip Sync](peer-to-peer-gossip-sync.md)
+- [Secure Peer Transport](secure-peer-transport.md)
+- [Peer-Confirmed Pruning](peer-confirmed-pruning.md)
+
+## Maintenance Rules
+
+- Keep one file per major feature.
+- Update feature docs when APIs, operations, or security controls change.
+- Cross-link each feature to [Runbook](../runbook.md) and [Security](../security.md).