refactor: centralize PR review agent profiles

[robbycochran]

Summary

• Centralize production PR-review agent profile selection in one case block.
• Remove repeated OpenCode/Codex lifecycle and workflow-selection conditionals.
• Keep OpenCode and Codex as the two production adapters.
• Document the Claude workflow as an offline configuration fixture, not a third production PR-review mode.

Validation

• go build ./...
• go vet ./...
• CGO_ENABLED=0 go test ./...
• make test-suite — 11/11 passed, 1 skipped
• actionlint, shellcheck, shell syntax, and git diff --check

This PR is labeled stackrox-ai-review so the merged Codex review flow can review it.

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[robbycochran]

Closing this PR because it targets the divergent refactor/workflow-code-layout branch; recreate it on main if the refactor is still needed.