fix(scripts): let the documentation site carry its own images

An image the manifest does not publish was rewritten to a raw.githubusercontent
URL, which serves a private repository to nobody: raw answers 404 unauthenticated,
and a github.com session does not authenticate it. Every image on the site was
broken for every reader, and no gate could say so — link checking asks whether
the file exists in the repository, not whether a site reader can fetch it.

The projector now copies a referenced image into the generated tree beside the
page and points the reference at it, so Vite bundles it like any other site
asset and repository visibility cannot reach the published page. The copy lands
beside the page so one relative URL is right from both locale trees and a page's
assets leave with the page; two sources projecting onto one path throw rather
than letting the last copy win.

Canonical Markdown keeps writing ordinary repository-relative paths, so the same
file still renders when read in the repository.

The guide this was found through is renamed to its subject: 配置模型.

docs/user/guide/providers.md

@@ -1,4 +1,4 @@
-# Configure model providers
+# Configure models
 
 English | [中文](providers.zh.md)