docs(site): add Continuous AI intro slide deck

[jamesadevine]

Summary

Adds a short (~7-slide) intro presentation for ado-aw — Continuous AI for Azure DevOps, built with Slidev and integrated into the docs site.

The deck's narrative:

1. CI/CD — the established rung we already trust (async, triggered, runs on existing runners, reliable).
2. Continuous AI — the next rung, inheriting the same operational properties but swapping deterministic scripts for an agent that reasons.
3. ado-aw — a platform for Continuous AI: author agents in markdown, compile to a secure Azure DevOps pipeline (shown side by side).
4. Key principles — markdown-first authoring, safe outputs, network isolation, threat detection, reuse of existing pipelines, gh-aw parity.
5. How it works — the three-stage zero-trust chain (Agent → Detection → SafeOutputs).

Where it lives

• Source: site/slides/ (Slidev project — slides.md + style.css, branded to match the docs palette).
• Build wiring: cd site && npm run build now runs build:slides (slidev build --base /ado-aw/slides/ --out ../public/slides) before astro build, so the static deck is published alongside the docs at /ado-aw/slides/.
• It is an unadvertised feature — nothing in the docs links to it (by design).
• Generated output (public/slides/, slides/node_modules/, slides/dist/) is git-ignored.

Presenter mode

The static build includes presenter view (notes, timer, next-slide preview) and a 404.html SPA fallback so deep links resolve on GitHub Pages. Live cross-device remote control still requires the dev server (npm run dev).

Test plan

• cd site && npm run build — full integrated build succeeds; starlight-links-validator reports all internal links valid.
• Verified deck output in site/dist/slides/: index.html, SPA-fallback 404.html, and the presenter-*.js chunk are all present, with assets correctly based at /ado-aw/slides/.
• Reviewed all 7 rendered slides via PNG export (including the side-by-side markdown/YAML slide and the Mermaid three-stage diagram).
• npm run export produces a 7-page dist/ado-aw-intro.pdf (verified page count).