fix: use getTagSlug() for tag links to prevent empty tag pages

Tags containing both spaces and dashes (e.g. "Writings - 創作") produced
mismatched slugs: inline generation created "writings---創作" while
getTagSlug() collapsed dashes to "writings-創作", causing tag pages to
show no articles.

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

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
+import "./.next/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.