feat: add fediverse_creator handle for Mastodon attribution

Expose a per-post fediverse_creator frontmatter field plus a site-wide
default in config.toml ([site].fediverse_creator). The handle is returned
in the post and site payloads, rendered as <dc:creator> in the RSS feed
and as authors[].name in the JSON feed, so a front-end can drop it into
<meta name="fediverse:creator"> on rendered pages. Per-post value
overrides the site default. Validated against a simple @user@host regex.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

test/server_test.rb

@@ -98,7 +98,7 @@ class ServerTest < Minitest::Test
     assert_predicate last_response, :ok?
     assert_equal "application/rss+xml", last_response["Content-Type"]&.split(";")&.first
     body = last_response.body
-    assert_includes body, "<rss version=\"2.0\">"
+    assert_includes body, "<rss version=\"2.0\""
     assert_includes body, "<title>Hello</title>"
     refute_includes body, "Draft"
     assert_includes body, "<language>en</language>"
@@ -154,6 +154,102 @@ class ServerTest < Minitest::Test
     refute_includes data["items"].map { |i| i["title"] }, "Draft"
   end
 
+  def test_post_summary_exposes_fediverse_creator
+    File.write(File.join(@dir, "attributed.md"), <<~POST)
+      +++
+      title = "Attributed"
+      slug = "attributed"
+      fediverse_creator = "@ada@lovelace.org"
+      +++
+
+      Body.
+    POST
+    get "/api/volumen/posts/attributed"
+    assert_predicate last_response, :ok?
+    data = JSON.parse(last_response.body)
+    assert_equal "@ada@lovelace.org", data["fediverse_creator"]
+  end
+
+  def test_post_summary_fediverse_creator_is_null_when_not_set
+    get "/api/volumen/posts/hello"
+    assert_predicate last_response, :ok?
+    assert_nil JSON.parse(last_response.body)["fediverse_creator"]
+  end
+
+  def test_posts_list_summary_exposes_fediverse_creator
+    File.write(File.join(@dir, "fed.md"), <<~POST)
+      +++
+      title = "Fed"
+      slug = "fed"
+      fediverse_creator = "@user@example.social"
+      +++
+
+      Body.
+    POST
+    get "/api/volumen/posts"
+    data = JSON.parse(last_response.body)
+    fed = data["posts"].find { |post| post["slug"] == "fed" }
+    assert_equal "@user@example.social", fed["fediverse_creator"]
+  end
+
+  def test_site_endpoint_exposes_fediverse_creator_default
+    get "/api/volumen/site"
+    assert_predicate last_response, :ok?
+    assert JSON.parse(last_response.body).key?("fediverse_creator")
+  end
+
+  def test_rss_feed_includes_dc_creator_when_set
+    File.write(File.join(@dir, "rss.md"), <<~POST)
+      +++
+      title = "Rss"
+      slug = "rss"
+      fediverse_creator = "@rss@example.com"
+      +++
+
+      Body.
+    POST
+    get "/api/volumen/feed.xml"
+    assert_includes last_response.body, "<dc:creator>@rss@example.com</dc:creator>"
+    assert_includes last_response.body, "xmlns:dc=\"http://purl.org/dc/elements/1.1/\""
+  end
+
+  def test_rss_feed_omits_dc_creator_when_not_set
+    get "/api/volumen/feed.xml"
+    refute_includes last_response.body, "<dc:creator>"
+  end
+
+  def test_json_feed_includes_authors_from_post
+    File.write(File.join(@dir, "jsonfed.md"), <<~POST)
+      +++
+      title = "Jsonfed"
+      slug = "jsonfed"
+      fediverse_creator = "@jf@example.io"
+      +++
+
+      Body.
+    POST
+    get "/api/volumen/feed.json"
+    item = JSON.parse(last_response.body)["items"].find { |i| i["id"] == "https://example.com/jsonfed" }
+    assert_equal [{ "name" => "@jf@example.io" }], item["authors"]
+  end
+
+  def test_json_feed_falls_back_to_site_default_fediverse_creator
+    Dir.chdir(@dir) do
+      File.write("config.toml", <<~TOML)
+        [site]
+        fediverse_creator = "@owner@example.com"
+      TOML
+    end
+    @config = Volumen::Config.load(
+      path: File.join(@dir, "config.toml"),
+      overrides: { content: @dir }
+    )
+    get "/api/volumen/feed.json"
+    items = JSON.parse(last_response.body)["items"]
+    expected = [{ "name" => "@owner@example.com" }]
+    assert(items.all? { |i| i["authors"] == expected })
+  end
+
   def test_search_by_title
     get "/api/volumen/posts?q=Hello"
     data = JSON.parse(last_response.body)