Add pagination to category, tag, and issue pages (10 per page)

pagerSize set to 10 (5 columns × 2 rows). New pagination partial
renders prev/next links and numbered page buttons. Applied to
_default/list.html (categories + tags) and issues/list.html.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hugo.toml

@@ -4,7 +4,7 @@ title = "Roux"
 enableRobotsTXT = true
 enableGitInfo = false
 [pagination]
-pagerSize = 200
+pagerSize = 10
 
 [taxonomies]
 category = "categories"