docs(redirects): document redirect_files bulk JSON option

Explain the new `redirect_files` option, both accepted JSON shapes
(object map and array of source/target objects), path resolution, and
precedence with inline `redirect_maps`.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Netdocs

docs-site/docs/plugins/redirects.md

@@ -11,7 +11,8 @@ for vanity links and for preserving inbound links after restructuring.
 
 | Option | Type | Default | Description |
 |---|---|---|---|
-| `redirect_maps` | object | — | Map of source path → destination URL. |
+| `redirect_maps` | object | — | Inline map of source path → destination URL. |
+| `redirect_files` | string \| array | — | One or more JSON files holding bulk redirects. |
 
 ```json
 {
@@ -28,6 +29,49 @@ for vanity links and for preserving inbound links after restructuring.
 Each key becomes an HTML page (e.g. `site/discord/index.html`) that immediately redirects
 to the mapped destination. Destinations may be absolute URLs or site-relative paths.
 
+## Bulk redirects from JSON file(s)
+
+Inline maps are convenient for a handful of entries, but migration redirect tables can run
+to hundreds of rows. Keep those in one or more JSON files and point `redirect_files` at them.
+The value may be a single path or an array of paths. Paths resolve against the project root
+first, then the docs directory, then as an absolute path.
+
+```json
+{
+  "name": "redirects",
+  "options": {
+    "redirect_files": ["redirects/blog.json", "redirects/legacy.json"]
+  }
+}
+```
+
+Each file may use either shape:
+
+**Object map** — source path → destination URL:
+
+```json
+{
+  "blog/2018/ls--how-to-turn-on-the-alternator/": "/blog/2018/ls-how-to-turn-on-the-alternator/",
+  "old/page/": "/new/page/"
+}
+```
+
+**Array of objects** — `source`/`target` (aliases `from`/`to` and `old`/`new` are also
+accepted). An optional `status` field is allowed for documentation/tooling but is ignored
+by the client-side redirect (a `meta refresh` cannot set an HTTP status code):
+
+```json
+[
+  { "source": "old/x/", "target": "/new/x/", "status": 308 },
+  { "from": "old/y/", "to": "/new/y/" }
+]
+```
+
+Files load first, then inline `redirect_maps` — so an inline entry overrides a file entry
+with the same source. Sources with a leading slash are normalized relative to the site
+directory. A missing or malformed file logs a warning and is skipped rather than failing the
+build.
+
 ## Attribution
 
 Behavior is modeled on [mkdocs-redirects](https://github.com/mkdocs/mkdocs-redirects) (MIT). See [Attributions](../about/attributions.md).