fix(site): replace Page not found nav item with GitHub repo link

Minima's header lists every titled page, so 404.html appeared in the menu.
Override the header to show a single link to the repository, and make the
404 page's home link respect baseurl.

404.html

@@ -7,7 +7,7 @@ permalink: /404.html
 <h1>Page not found</h1>
 
 <p>That page does not exist. The provider list lives on the
-<a href="/">home page</a>.</p>
+<a href="{{ "/" | relative_url }}">home page</a>.</p>
 
 <p>If a link here is broken,
-<a href="https://github.com/tiennm99/penny-pincher-provider/issues/new">open an issue</a>.</p>
+<a href="https://github.com/{{ site.repository }}/issues/new">open an issue</a>.</p>

_config.yml

@@ -3,6 +3,9 @@ description: A curated list of affordable (or almost free) LLM providers
 theme: minima
 show_downloads: false
 
+# Linked from the header nav (_includes/header.html) and 404.html.
+repository: tiennm99/penny-pincher-provider
+
 # GitHub Pages target. It only ever reads this file, so its values live here and
 # Cloudflare overrides them via _config.cloudflare.yml.
 url: https://tiennm99.github.io

_includes/header.html

@@ -0,0 +1,27 @@
+{%- comment -%}
+  Overrides minima's header. Its default nav lists every titled page, which
+  surfaced 404.html as a "Page not found" menu item; this nav links the repo.
+{%- endcomment -%}
+<header class="site-header" role="banner">
+
+  <div class="wrapper">
+    <a class="site-title" rel="author" href="{{ "/" | relative_url }}">{{ site.title | escape }}</a>
+
+    {%- if site.repository -%}
+      <nav class="site-nav">
+        <input type="checkbox" id="nav-trigger" class="nav-trigger" />
+        <label for="nav-trigger">
+          <span class="menu-icon">
+            <svg viewBox="0 0 18 15" width="18px" height="15px">
+              <path d="M18,1.484c0,0.82-0.665,1.484-1.484,1.484H1.484C0.665,2.969,0,2.304,0,1.484l0,0C0,0.665,0.665,0,1.484,0 h15.032C17.335,0,18,0.665,18,1.484L18,1.484z M18,7.516C18,8.335,17.335,9,16.516,9H1.484C0.665,9,0,8.335,0,7.516l0,0 c0-0.82,0.665-1.484,1.484-1.484h15.032C17.335,6.031,18,6.696,18,7.516L18,7.516z M18,13.516C18,14.335,17.335,15,16.516,15H1.484 C0.665,15,0,14.335,0,13.516l0,0c0-0.82,0.665-1.483,1.484-1.483h15.032C17.335,12.031,18,12.695,18,13.516L18,13.516z"/>
+            </svg>
+          </span>
+        </label>
+
+        <div class="trigger">
+          <a class="page-link" href="https://github.com/{{ site.repository }}">GitHub</a>
+        </div>
+      </nav>
+    {%- endif -%}
+  </div>
+</header>

docs/deployment.md

@@ -96,5 +96,8 @@ which a Git-connected project rejects. Push to `main` instead.
   content, pulled into `index.md` by `include_relative`, which reads excluded files
   fine — the exclusion only stops the raw markdown shipping as a duplicate page.
 - `404.html` is served automatically by both hosts for unmatched routes.
+- `_includes/header.html` overrides minima's header. The stock nav lists every page
+  with a `title`, which put `404.html` in the menu as "Page not found"; the override
+  shows a single GitHub link built from `repository` in `_config.yml`.
 - Ruby is pinned to the `3.4` series in both workflows rather than an exact patch.
   Cloudflare's own build image is irrelevant here, since Actions does the building.