Add codex socket cancel integration coverage

[cweill]

Motivation

Add socket-level coverage for codex cancel so mimic's e2e suite exercises the cancel RPC against a real codex session. While doing that, factor the root integration test setup into helpers so new socket e2e cases do not duplicate process bootstrap.

Summary

• extract buildMimic, spawnMimic, waitForSocket, waitForWireState, and rpc in main_integration_test.go
• update the existing socket submit/complete test to use the shared helpers
• add TestIntegration_MimicSocketCodexCancel that submits a long codex prompt, waits for working, sends socket cancel, and asserts the wire state becomes complete

Testing

• go build ./...
• go vet ./...
• Not run in this clone: go test -tags=integration -run 'TestIntegration_MimicSocket(SubmitAndComplete|CodexCancel)$' ./

Review focus

• confirm the shared helpers keep the root e2e tests reusable without changing the //go:build integration behavior
• confirm the cancel assertion matches the dispatcher contract for interrupted codex work: wire-state complete

Closes LAB-1263

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[cweill]

Addressed the blocking workflow failure from issue comment 4250245468 in 3303a71.

• .github/workflows/claude-code-review.yml now skips cleanly when neither ANTHROPIC_API_KEY nor CLAUDE_CODE_OAUTH_TOKEN is configured, instead of hard-failing the PR check.
• The review workflow now supports both auth inputs, matching the action's supported configuration.
• .github/workflows/claude.yml was updated the same way so manual @claude runs don't fail for the same repo-level secret misconfiguration.