[codex] Add agent infrastructure documentation

[LarytheLord]

What changed

• added a new Infrastructure/README.md guide for clean-room agent runtime patterns across Open Paws projects
• linked the new infrastructure section from the root documentation index
• updated CLAUDE.md so contributors can discover the new docs alongside the existing knowledge, prediction, generation, and automation sections

Why

We now have agent-related implementation work happening across the scanner, platform, and tooling repos. This PR gives those efforts a shared architecture document and records the clean-room reuse policy so future work stays aligned.

Impact

• contributors have one place to understand how scanner export, quest ingestion, and tool-sensitivity work fit together
• the organization has a documented boundary between reusable product patterns and copied proprietary code
• future repo work can plug into a shared runtime direction instead of growing in isolation

Validation

• git diff --check

Notes

• this is documentation-only and does not change application behavior

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