add tag cloud layout for /tags/ page

New terms.html template renders tags as pills with article counts
instead of the generic list view with dates and read-more links.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

layouts/_default/terms.html

@@ -0,0 +1,15 @@
+{{ define "main" }}
+<div style="max-width:48rem;margin:0 auto;padding:3rem 1rem">
+  <h1 style="font-family:var(--ifk-font);font-size:2.75rem;font-weight:600;margin-bottom:2rem">
+    {{ .Title }}
+  </h1>
+  <div style="display:flex;flex-wrap:wrap;gap:0.75rem">
+    {{ range .Pages }}
+    <a href="{{ .Permalink }}" style="display:inline-flex;align-items:center;gap:0.5rem;padding:0.5rem 1.25rem;background:#f8fafc;border:1px solid #e2e8f0;border-radius:999px;text-decoration:none;color:var(--ifk-text);font-family:system-ui,sans-serif;font-size:0.9rem;transition:all 0.15s">
+      <span style="font-weight:600">{{ .Title }}</span>
+      <span style="background:var(--ifk-accent);color:#fff;font-size:0.7rem;font-weight:700;padding:0.15rem 0.5rem;border-radius:999px;min-width:1.25rem;text-align:center">{{ len .Pages }}</span>
+    </a>
+    {{ end }}
+  </div>
+</div>
+{{ end }}