[deep-report] quick-start.mdx: collapse per-engine authentication steps into accordion/tabs

### Description
`docs/src/content/docs/setup/quick-start.mdx` lines 119-159 ("Configuring authentication") lists full setup instructions for all 5 engines (Copilot, Claude, Codex, Gemini, Pi) back-to-back as flat bold headers. A beginner following the guide for one engine has to scroll past 4 irrelevant engine setups. Verified still present in current source — no tabs or `` accordion wrapping.

### Expected Impact
Wrapping each engine's auth steps in a `` accordion (or tabbed component) so only the reader's chosen engine is expanded by default reduces scroll fatigue for first-time users, per the Documentation Noob Test Report.

### Suggested Agent
Docs-focused agent / Documentation Noob Tester follow-up.

### Estimated Effort
Quick (< 1 hour)

### Data Source
DeepReport Intelligence Briefing analysis run, 2026-09-15, based on Documentation Noob Test Report discussion #61022. Verified live against `docs/src/content/docs/setup/quick-start.mdx:119-159` before filing — no existing open issue covers this specific gap.

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `api.anthropic.com`
>
> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "api.anthropic.com"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [🔬 Deep Report](https://github.com/github/gh-aw/actions/runs/34937799028) · claude · agent · 248 AIC · ⌖ 10.3 AIC · ⊞ 12.8K · [◷](https://github.com/search?q=repo%3Agithub%2Fgh-aw+is%3Aissue+%22gh-aw-workflow-call-id%3A+github%2Fgh-aw%2Fdeep-report%22&type=issues)
> - [x] expires on Sep 16, 2026, 10:52 PM UTC-08:00

Open docs/src/content/docs/setup/quick-start.mdx and inspect lines 119-159, the “Configuring authentication” section. Group the Copilot, Claude, Codex, Gemini, and Pi instructions into accordion or tabbed sections, with the chosen engine easy to expand. Done when the five setups are no longer presented as one flat sequence and the quick-start guide remains readable for each engine.

Written by the indexing model from the issue text.