[blog] Add Doris Summit 2026 recap (#4608)

Publish the complete English Doris Summit 2026 recap at
`/blog/doris-summit-2026-recap`, authored by Apache Doris · Mingyu Chen
and dated November 11, 2026, with the recap video at the start of the
article.

The article includes four compressed content images, an 1800 × 766
cover, and a local video poster. It preserves the supplied text and
recording links and includes the required metadata, image alt text, and
ASF license header.

The reusable `YouTube` component initially shows the local poster and a
play button. Activation creates the YouTube iframe in place, so the
initial page makes no YouTube requests. The component uses existing
theme tokens, supports keyboard activation and focus transfer, and
provides a direct YouTube link. It adds no dependencies or video
binaries. Registering it in the MDX component map makes it available to
other MDX pages; converting this post to `.mdx` preserves its URL.

## Validation

- Article link lint passed without errors or warnings; external links
were reported without fetching. SEO lint reported no findings.
- Confirmed the original body and publication metadata are preserved and
local image references resolve.
- Development server compiled successfully; the article, cover, and
activated YouTube embed returned HTTP 200.
- Automated local Chrome checks confirmed zero YouTube requests before
activation, keyboard activation and focus transfer, responsive desktop
and mobile layouts, theme token rendering across eight brand themes, and
no page JavaScript errors.
- Inspected desktop and mobile screenshots.
- `git diff --check` passed. No production build was run, following
`doc-tools/HOW-TO-ADD-BLOG.md`.

## Versions

Not applicable: this is a Blog post and a shared MDX component; there
are no versioned documentation content changes.

- [ ] dev
- [ ] 4.x
- [ ] 3.x
- [ ] 2.1 or older (not covered by version/language sync gate)

## Languages

- [ ] Chinese
- [x] English

The request covers the English article only. No translated post or
versioned documentation counterparts are required. The shared component
marks its interface strings for translation through Docusaurus.

## Docs Checklist

- [x] Checked by AI
- [ ] Test Cases Built
- [x] Updated required version and language counterparts, or explained
why not
- [x] If only one language changed, confirmed whether source/translation
counterparts need sync

Validation used static checks and an automated local browser check; no
permanent test files were added. Blog discovery is automatic, and the
article URL is unchanged.

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Co-authored-by: morningman <moringman@apache.org>