feat(wpcarro/blog): Add a blog index page

TL;DR:
- Create an index page to list blog posts
- Drop blog.wpcarro.dev -> wpcarro.dev/blog
- Create fragments directory to host reusable static website components
- Consume fragments in wpcarro.dev and wpcarro.dev/blog for brand consistency

Change-Id: Ib8440300c008c3c0c5e5a6f207e4ea207dd41b47
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4717
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/website/default.nix

@@ -1,13 +1,27 @@
 { pkgs, depot, ... }:
 
-pkgs.stdenv.mkDerivation {
-  name = "wpcarro.dev";
-  src = builtins.path { path = ./.; name = "website"; };
-  installPhase = ''
-    mkdir -p $out
-    cp $src/index.html $out
+rec {
+  inherit (depot.users) wpcarro;
 
-    mkdir -p $out/habits
-    cp -r ${depot.users.wpcarro.website.habit-screens} $out/habits/index.html
-  '';
+  header = "${./fragments/header.html}";
+  footer = "${./fragments/footer.html}";
+  addendum = "${./fragments/addendum.html}";
+
+  root = pkgs.stdenv.mkDerivation {
+    name = "wpcarro.dev";
+    src = builtins.path { path = ./.; name = "website"; };
+    installPhase = ''
+      mkdir -p $out
+
+      cat ${header} \
+          ${./fragments/homepage.html} \
+          ${footer} \
+          ${addendum} > $out/index.html
+
+      mkdir -p $out/habits
+      cp -r ${wpcarro.website.habit-screens} $out/habits/index.html
+
+      cp -r ${wpcarro.website.blog.root} $out/blog
+    '';
+  };
 }