feat: add fulltext search with ?q= parameter

Filter posts by case-insensitive match in title and body. Extracted
filter_by_lang and search_posts helpers to keep complexity in check.

CHANGELOG.md

@@ -30,6 +30,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - CSRF protection on `POST /admin/preview`.
 - Symlink-safe containment in `Store#media_file` via `File.realpath`.
 
+### Added
+
+- **Scheduled publishing:** a `publish_at` frontmatter field hides posts from the
+  public API and feeds until their publication date arrives. The admin form
+  includes a Publish at date picker.
+- **JSON Feed:** `GET /api/volumen/feed.json` serves a jsonfeed.org v1.1 feed
+  with `content_html` and `date_published` per item.
+- **Fulltext search:** `GET /api/volumen/posts?q=…` filters posts by
+  case-insensitive match in title and body.
+
 ### Changed
 
 - Split `lib/volumen/server.rb` into `api_routes.rb` and `admin_routes.rb` modules,

lib/volumen/server.rb

@@ -102,14 +102,29 @@ module Volumen
 
     def filtered_posts
       posts = published_posts
-      if params["lang"]
+      posts = filter_by_lang(posts)
-        lang = params["lang"]
-        posts = posts.select { |post| post.lang == lang || post.all_langs? }
-      end
       posts = posts.select { |post| post.tags.include?(params["tag"]) } if params["tag"]
+      posts = search_posts(posts) if params["q"]
       posts
     end
 
+    def filter_by_lang(posts)
+      return posts unless params["lang"]
+
+      lang = params["lang"]
+      posts.select { |post| post.lang == lang || post.all_langs? }
+    end
+
+    def search_posts(posts)
+      query = params["q"].to_s.strip.downcase
+      return posts if query.empty?
+
+      posts.select do |post|
+        post.title.to_s.downcase.include?(query) ||
+          post.body.downcase.include?(query)
+      end
+    end
+
     def tag_counts
       counts = Hash.new(0)
       published_posts.each { |post| post.tags.each { |tag| counts[tag] += 1 } }

test/server_test.rb

@@ -153,4 +153,29 @@ class ServerTest < Minitest::Test
     assert_includes data["items"].first["content_html"], "<strong>world</strong>"
     refute_includes data["items"].map { |i| i["title"] }, "Draft"
   end
+
+  def test_search_by_title
+    get "/api/volumen/posts?q=Hello"
+    data = JSON.parse(last_response.body)
+    assert_equal 1, data["total"]
+    assert_equal "hello", data["posts"].first["slug"]
+  end
+
+  def test_search_by_body
+    get "/api/volumen/posts?q=world"
+    data = JSON.parse(last_response.body)
+    assert_equal 1, data["total"]
+  end
+
+  def test_search_no_match
+    get "/api/volumen/posts?q=nonexistent"
+    data = JSON.parse(last_response.body)
+    assert_equal 0, data["total"]
+  end
+
+  def test_search_is_case_insensitive
+    get "/api/volumen/posts?q=HELLO"
+    data = JSON.parse(last_response.body)
+    assert_equal 1, data["total"]
+  end
 end