chore: prepare release v0.4.0

docs/api-reference.md

@@ -33,6 +33,7 @@ Posts with `all_langs = true` in their frontmatter match every `lang` filter.
 |-------|--------|---------|--------------------|
 | lang  | string | —       | Filter by language |
 | tag   | string | —       | Filter by tag      |
+| q     | string | —       | Case-insensitive search across title and body |
 | page  | int    | 1       | Page number        |
 | limit | int    | 20      | Per page (1–100)   |
 
@@ -41,6 +42,8 @@ Posts with `all_langs = true` in their frontmatter match every `lang` filter.
   "page": 1,
   "page_size": 20,
   "total": 1,
+  "has_next": false,
+  "has_prev": false,
   "posts": [
     {
       "slug": "hello",
@@ -64,7 +67,7 @@ Posts with `all_langs = true` in their frontmatter match every `lang` filter.
 
 Single post including the raw Markdown body and rendered HTML. Optional
 `?lang=` selects a translation. Returns `404` with `{"error":"not_found"}` if
-no match.
+no match. Drafts return `404` with `{"error":"draft"}`.
 
 ```json
 {
@@ -93,7 +96,14 @@ Tag cloud with counts (published posts only), most frequent first.
 { "tags": [{ "name": "intro", "count": 1 }] }
 ```
 
-## `GET /api/volumen/feed.xml`, `GET /api/volumen/sitemap.xml`
+## `GET /api/volumen/feed.xml`, `GET /api/volumen/feed.json`, `GET /api/volumen/sitemap.xml`
 
-RSS 2.0 feed (latest 20 posts) and a sitemap of post URLs, built from
-`site.base_url`.
+- `feed.xml` — RSS 2.0 feed of the 20 most recent posts.
+- `feed.json` — [JSON Feed 1.1](https://www.jsonfeed.org/) document with
+  `content_html` and `date_published` per item.
+- `sitemap.xml` — XML sitemap built from `site.base_url`.
+
+## `OPTIONS /api/volumen/*`
+
+Preflight requests return an empty `204` with the same CORS headers as the GET
+endpoints, so browsers can reach the JSON API cross-origin.