posts: factor out post navbar into component.

* Factor out the post navbar into a component. The post navbar is the
  part of the post containing the current search, the list of pools, and
  the list of favgroups, along with next/prev navigation links.

* Change navbar markup: remove various unused CSS classes/IDs, change
  pools to use same markup as favgroups, replace nested <div>'s with
  flat <ul>/<li> list.

* Use CSS to truncate long searches/pool names/favgroup names if they're
  too wide for the screen (especially on mobile).

test/components/post_navbar_component_test.rb

@@ -0,0 +1,52 @@
+require "test_helper"
+
+class PostNavbarComponentTest < ViewComponent::TestCase
+  def render_post_navbar(post, **options)
+    render_inline(PostNavbarComponent.new(post: post, **options))
+  end
+
+  setup do
+    @post = create(:post)
+    @user = create(:user)
+  end
+
+  context "The PostNavbarComponent" do
+    context "for a post with a search" do
+      should "render" do
+        render_post_navbar(@post, current_user: @user, search: "touhou")
+
+        assert_css(".search-navbar", text: "Search: touhou")
+      end
+    end
+
+    context "for a post with pools" do
+      should "render" do
+        as(@user) do
+          @pool1 = create(:pool, category: "series")
+          @pool2 = create(:pool, category: "collection")
+          @post.update(tag_string: "pool:#{@pool1.id} pool:#{@pool2.id}")
+        end
+
+        render_post_navbar(@post, current_user: @user, pool_id: @pool1.id)
+
+        assert_css(".pool-name", text: "Pool: #{@pool1.pretty_name}")
+        assert_css(".pool-name", text: "Pool: #{@pool2.pretty_name}")
+      end
+    end
+
+    context "for a post with favgroups" do
+      should "render" do
+        as(@user) do
+          @favgroup1 = create(:favorite_group, creator: @user)
+          @favgroup2 = create(:favorite_group, creator: @user)
+          @post.update(tag_string: "favgroup:#{@favgroup1.id} favgroup:#{@favgroup2.id}")
+        end
+
+        render_post_navbar(@post, current_user: @user, favgroup_id: @favgroup1.id)
+
+        assert_css(".favgroup-name", text: "Favgroup: #{@favgroup1.pretty_name}")
+        assert_css(".favgroup-name", text: "Favgroup: #{@favgroup2.pretty_name}")
+      end
+    end
+  end
+end

test/functional/posts_controller_test.rb

@@ -556,7 +556,7 @@ class PostsControllerTest < ActionDispatch::IntegrationTest
           get post_path(@post)
 
           assert_response :success
-          assert_select "#pool-nav .pool-name", /Pool: comic/
+          assert_select ".pool-navbar .pool-name", /Pool: comic/
         end
       end