Add RSS subscribe links with icon across blog pages, footer, and head

- Add <.rss_icon> inline SVG component in core_components.ex
- Inject RSS <link> tags into <head> on blog pages for auto-discovery
- Show RSS icon next to blog title on index and tag pages
- Show RSS icon on post pages next to back-link
- Add Subscribe section in footer with links to both feeds
- Wire feed URL through blog controller (index, show, tag actions)

174 tests pass, credo clean.

app/lib/firehose_web/controllers/blog_controller.ex

@@ -9,9 +9,11 @@ defmodule FirehoseWeb.BlogController do
     result = blog.paginate(page)
 
     meta = Blogex.SEO.meta_tags_for_blog(blog, FirehoseWeb.Endpoint.url())
+    rss_url = rss_feed_url(blog)
 
     conn
     |> FirehoseWeb.Layouts.put_content_for(:meta_tags, meta)
+    |> FirehoseWeb.Layouts.put_content_for(:feed_links, %{rss_url: rss_url, title: blog.title()})
     |> render(:index,
       page_title: blog.title(),
       blog_title: blog.title(),
@@ -19,7 +21,8 @@ defmodule FirehoseWeb.BlogController do
       posts: result.entries,
       base_path: blog.base_path(),
       page: result.page,
-      total_pages: result.total_pages
+      total_pages: result.total_pages,
+      rss_feed_url: rss_url
     )
   end
 
@@ -27,31 +30,40 @@ defmodule FirehoseWeb.BlogController do
     blog = conn.assigns.blog
     post = blog.get_post!(slug)
     visibility = Blogex.Post.visibility(post)
+    rss_url = rss_feed_url(blog)
 
     meta = Blogex.SEO.meta_tags(post, FirehoseWeb.Endpoint.url(), blog)
 
     conn
     |> FirehoseWeb.Layouts.put_content_for(:meta_tags, meta)
+    |> FirehoseWeb.Layouts.put_content_for(:feed_links, %{rss_url: rss_url, title: blog.title()})
     |> render(:show,
       page_title: post.title,
       post: post,
       meta: meta,
       base_path: blog.base_path(),
       visibility: visibility,
-      authenticated: !!(conn.assigns[:current_scope] && conn.assigns.current_scope.user)
+      authenticated: !!(conn.assigns[:current_scope] && conn.assigns.current_scope.user),
+      rss_feed_url: rss_url
     )
   end
 
   def tag(conn, %{"tag" => tag}) do
     blog = conn.assigns.blog
     posts = blog.posts_by_tag(tag)
+    rss_url = rss_feed_url(blog)
 
-    render(conn, :tag,
+    rss_link = %{rss_url: rss_url, title: blog.title()}
+
+    conn
+    |> FirehoseWeb.Layouts.put_content_for(:feed_links, rss_link)
+    |> render(:tag,
       page_title: "#{blog.title()} — #{tag}",
       blog_title: blog.title(),
       tag: tag,
       posts: posts,
-      base_path: blog.base_path()
+      base_path: blog.base_path(),
+      rss_feed_url: rss_url
     )
   end
 
@@ -77,4 +89,9 @@ defmodule FirehoseWeb.BlogController do
       _ -> 1
     end
   end
+
+  defp rss_feed_url(blog) do
+    base_id = blog.base_path() |> String.trim_leading("/blog/")
+    FirehoseWeb.Endpoint.url() <> "/api/blog/#{base_id}/feed.xml"
+  end
 end