docs: add build/test commands and architecture overview to CLAUDE.md

[9Pie-893]

Expand CLAUDE.md beyond the existing AGENTS.md import with a Commands section (build, test, single-test invocations, e2e, lint/format, Go SDK CI) sourced from tasks/.toml, and an Architecture section synthesizing the control-plane/data-plane split, egress policy enforcement path, gateway RPC authorization/interceptors, OCSF logging, and proto/SDK relationships from architecture/.md.

Summary

• 1-3 sentences: what this PR does and why

Related Issue

• Required for features, user-visible behavior changes, public API changes,
  architecture changes, and multi-PR efforts: Fixes #NNN or Closes #NNN.
  For an exempt small docs fix, mechanical change, or obvious localized bug fix:
  No issue required:

Changes

• Bullet list of key changes -->

Testing

• Report current verification performed for this implementation. Do not copy diagnostics from the original issue. -->
• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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