Drop PaperMod theme, use minimal self-contained templates

PaperMod's opengraph.html calls partial with a redundant "partials/"
prefix that the production Hugo version (0.154.5, from the
hugomods/hugo:exts build image) doesn't tolerate, breaking the build.
Rather than patch a vendored theme, replaced it with plain, dependency-
free layouts (baseof/index/single/list) that render the actual homepage
content directly. Verified building successfully against the exact
Hugo image/version the deploy pipeline uses.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

layouts/index.html

@@ -1,16 +1,10 @@
-{{- define "main" }}
-<section class="hero">
-  {{- with .Params.hero_heading }}
-  <h1 class="hero-heading">{{ . }}</h1>
-  {{- end }}
-  {{- with .Params.hero_subheading }}
-  <p class="hero-subheading">{{ . }}</p>
-  {{- end }}
-  {{- with .Params.intro }}
-  <div class="hero-intro">{{ . | markdownify }}</div>
-  {{- end }}
-  {{- if .Params.cta_text }}
-  <a class="hero-cta" href="{{ .Params.cta_link }}">{{ .Params.cta_text }}</a>
-  {{- end }}
-</section>
-{{- end }}
+{{ define "main" }}
+<h1 style="font-size:2.25rem; margin-bottom:0.5rem;">{{ .Params.hero_heading }}</h1>
+<p style="font-size:1.15rem; opacity:0.85; margin-top:0;">{{ .Params.hero_subheading }}</p>
+<div style="margin-top:2rem;">{{ .Params.intro | markdownify }}</div>
+{{ with .Params.cta_text }}
+<p style="margin-top:2rem;">
+  <a href="{{ $.Params.cta_link }}" style="display:inline-block; padding:0.75rem 1.5rem; border-radius:0.4rem; background:#1a5fb4; color:#fff; text-decoration:none;">{{ . }}</a>
+</p>
+{{ end }}
+{{ end }}