docs(configure): repoint the dead /docs/build/objects link to /docs/build/data (#104)

`content/docs/configure/data-sources.mdx` linked to `/docs/build/objects`
in its "Where to go next" list. No such page exists and no redirect covers
it, so the link was a live 404 on a customer-facing page.

`/docs/build/objects` has never existed as a page in this repository's
history, so a redirect would be dead config: the four entries already in
`apps/docs/next.config.mjs` all cover URLs that were live and moved by the
Build restructure. Repointing is the correct route.

The target is `/docs/build/data` (`content/docs/build/data/index.mdx`),
which is the page that documents `ObjectSchema.create`. The link label
becomes "Data Model" to match that page's title and the convention used by
the other 19 English links to it.


Claude-Session: https://claude.ai/code/session_01CJPxtTxoxTUnjNdTbiEaRa

Co-authored-by: os-zhuang <zhuangjianguo@steedos.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: 3 people

content/docs/configure/data-sources.mdx

@@ -255,5 +255,5 @@ non-production copy first.
 - [Runtime](/docs/configure/runtime) — the primary database behind `default`
 - [AI Service](/docs/configure/ai) — chat, embeddings, RAG, MCP
 - [AI Agents](/docs/build/agents) — declarative agents over your objects
-- [Objects](/docs/build/objects) — the `ObjectSchema.create` authoring surface
+- [Data Model](/docs/build/data) — the `ObjectSchema.create` authoring surface
 - [`examples/app-crm` datasources](https://github.com/objectstack-ai/objectstack/tree/main/examples/app-crm/src/datasources) — a real datasource + routing example