[information-architecture] Refactor Opportunist is installed but missing from workflow discovery

## Information Architecture Findings

### 1. Refactor Opportunist is installed by continuous improvement setup but absent from public discovery paths
**Area:** Navigation / Grouping / Onboarding
**Component(s):** `scripts/quick-setup.sh`, `gh-agent-workflows/README.md`, `docs/workflows/gh-agent-workflows.md`, `mkdocs.yml`, `docs/workflows/gh-agent-workflows/`

**Problem:** Users who install the continuous improvement workflow set can receive `refactor-opportunist`, but the public documentation catalog and MkDocs navigation do not expose a Refactor Opportunist page or entry. That makes the installed workflow hard to rediscover, understand, or configure from the main docs UI.

**Evidence:**
- `scripts/quick-setup.sh:122-135` includes `refactor-opportunist` in `continuous_improvement_workflows`.
- `gh-agent-workflows/README.md:67-80` also lists `refactor-opportunist` under `--continuous-improvement`.
- `docs/workflows/gh-agent-workflows.md:26-27` lists the continuous improvement add-ons but omits `refactor-opportunist`.
- `docs/workflows/gh-agent-workflows.md:84-99` lists standalone scheduled workflows and omits Refactor Opportunist.
- `mkdocs.yml:45-68` lists Codebase Maintenance and Planning & Insights workflow navigation entries and omits Refactor Opportunist.
- `docs/workflows/gh-agent-workflows/*refactor*` has no matching public docs page, while the source README exists at `gh-agent-workflows/refactor-opportunist/README.md:1-37`.

**Suggested improvement:** Add a public Refactor Opportunist docs page, include it in `docs/workflows/gh-agent-workflows.md`, and add it to `mkdocs.yml` under the appropriate workflow group, likely Codebase Maintenance or Planning & Insights.

## Suggested Actions
- [ ] Add `docs/workflows/gh-agent-workflows/refactor-opportunist.md` or equivalent published docs for the workflow.
- [ ] Add Refactor Opportunist to the continuous improvement list and available workflow table in `docs/workflows/gh-agent-workflows.md`.
- [ ] Add Refactor Opportunist to the MkDocs Workflows navigation under the chosen category.

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Start with gh-agent-workflows/refactor-opportunist/README.md, then compare the referenced entries in docs/workflows/gh-agent-workflows.md and mkdocs.yml. Add the public Refactor Opportunist page and the requested catalog and navigation entries; done means the workflow is discoverable through the documentation UI and its existing source README is represented.

Written by the indexing model from the issue text.