docs: update lens reviewer criticality in README [doc-updater]

[james-in-a-box]

Update documentation to reflect changes from 08e8a7f:

• README.md described reviewer_security and reviewer_concurrency as "advisory" lens reviewers, but Reviewer roster reshape: remove subagent fan-out, promote lens reviewers to CRITICAL #2139 promoted both from ADVISORY to CRITICAL — a NACK from either now blocks consensus until the producer re-proposes.

The stale wording ("advisory security and concurrency lens reviewers") was the only doc inconsistency; docs/reference/agent-roles.md and docs/guides/concurrent-execution.md were already updated in the same commit.

Triggered by: #2152

Authored-by: egg

[egg-reviewer]

Approve. One-line doc fix; verified accurate.

Verification

• README.md:105 previously read "advisory security and concurrency lens reviewers add targeted cross-file analysis."
• PR #2139 (commit 08e8a7f) promoted reviewer_security and reviewer_concurrency from ADVISORY to CRITICAL and updated docs/reference/agent-roles.md and docs/guides/concurrent-execution.md, but missed README.md.
• Authoritative wording in docs/reference/agent-roles.md: "CRITICAL — a NACK blocks consensus until the producer re-proposes (#2139; promoted from ADVISORY)."
• Authoritative wording in docs/guides/concurrent-execution.md: "a NACK from either blocks consensus until the producer re-proposes (#2139)."
• New README wording — "block consensus on a NACK" — is consistent with both.

Other README mentions checked

• README.md:137 (✓ reviewer_security ✓ reviewer_concurrency in pipeline diagram) is unaffected — it just shows they ran, no criticality claim. No change needed.
• No other "advisory" references to these roles remain in README.md.

No blocking issues. CI is green except for the in-progress egg-reviewer check itself.

— Authored by egg

[james-in-a-box]

egg is addressing review feedback...

[james-in-a-box]

egg feedback addressed. View run logs

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