docs(site): put Docs first in the objectstack.ai top navigation (#28974)

Fixes #28973

## What changes

`apps/docs/lib/layout.shared.tsx`: `baseOptions().links` gains `{ text:
'Docs', url: '/docs', active: 'nested-url' }` as its first entry, so the
objectstack.ai top nav reads Docs, Why, Blog, Product. One file, +2
lines (the entry and a one-line comment).

## Why

The maintainer asked whether a nav without Docs made sense, agreed to
add it, and handed it to the docs lane (quoted on #28973). Why and Blog
lead to the www.objectos.ai blog and Product to www.objectos.ai, so
nothing in the nav reached this site's own `/docs`. Every layout spreads
this array (DocsLayout, and HomeLayout on home and `/blog`), so one
entry adds the link site-wide, and `nested-url` highlights it on every
docs page. Merging Why and Blog is left out, as the maintainer decided.

## Verification

- The entry has the same shape as the `Blog` entry beside it (`text`,
`url`, `active: 'nested-url'`). No test or script pins the links array
(`git grep` over `apps/docs`).
- CI `apps/docs` type-check and build run on this head. The deployed
site is checked after landing.

Clause-②: no
Metadata-protocol: none

## Human Minimum

- [x] 1. Schemas start as Zod; `packages/spec` holds no runtime logic.
(not touched)
- [x] 2. Every name I added uses the casing for its kind.
- [x] 3. No formatter ran; `pnpm lint` passes. (CI)
- [x] 4. One issue, one branch off an up-to-date `main`, one pull
request.
- [x] 5. A change that publishes carries a changeset, and both
declaration lines are filled in here and in the changeset. (`apps/docs`
does not publish)
- [x] 6. `packages/spec` touched: its generated artifacts are
regenerated and committed. (not touched)
- [x] 7. No hand edits to `content/docs/references/`,
`packages/*/CHANGELOG.md` or `content/docs/releases/`.
- [x] 8. Title, body and comments are in English.
- [x] The *Before Submitting* list in CONTRIBUTING.md is done.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01QsR2jTaZ2GeyfjANMwstiw

Co-authored-by: Claude <noreply@anthropic.com>

Author: objectstack-fleet[bot]

apps/docs/lib/layout.shared.tsx

@@ -47,6 +47,8 @@ export function baseOptions(): BaseLayoutProps {
     // `active` is matched against the PUBLIC pathname (`/blog/x`, never the `/en/blog/x`
     // a post is prerendered under) — `components/root-provider.tsx` supplies it.
     links: [
+      // This site's own docs come first: the other three lead off-site or to the blog.
+      { text: 'Docs', url: '/docs', active: 'nested-url' },
       { text: 'Why', url: ESSAY_URL, active: 'url' },
       { text: 'Blog', url: '/blog', active: 'nested-url' },
       // The product site, by role: ObjectOS (editions, pricing, blog) lives there.