[information-architecture] Core default workflow is filed under Repository Maintenance in docs nav

## Information Architecture Findings

### 1. Core workflow is grouped outside the Core hierarchy
**Area:** Grouping and hierarchy consistency
**Component(s):** `mkdocs.yml`, `docs/index.md`, `docs/workflows/gh-agent-workflows.md`, `scripts/quick-setup.sh`
**Problem:** The onboarding flow defines a **core default set** that includes `pr-actions-detective`, but the main docs navigation places that workflow under **Repository Maintenance** instead of **Core Workflows**. Users who install the default core set then navigate by the Core section cannot find one of the five installed workflows where they expect it, which breaks information scent during first-time setup.

**Evidence:**
- `scripts/quick-setup.sh:121-127` includes `pr-actions-detective` in `default_workflows`.
- `docs/workflows/gh-agent-workflows.md:28` lists `pr-actions-detective` in **Core (default)**.
- `docs/index.md:50-58` presents it as one of the five core workflows.
- `mkdocs.yml:30-34` defines **Core Workflows** nav entries without `pr-actions-detective`.
- `mkdocs.yml:35-41` places **PR Actions Detective** under **Repository Maintenance**.

**Suggested improvement:** Keep one taxonomy across onboarding and navigation by moving **PR Actions Detective** into the **Core Workflows** nav group (or, if intentionally non-core, update all core-set docs and install guidance to match that decision).

## Suggested Actions
- [ ] Update `mkdocs.yml` so `PR Actions Detective` appears in the `Core Workflows` group.
- [ ] Verify `docs/index.md`, `docs/workflows/gh-agent-workflows.md`, and `scripts/quick-setup.sh` all use the same core-set grouping terminology.
- [ ] Add a docs consistency check to flag workflows that are declared core but categorized elsewhere in top-level navigation.

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