chore(i18n): exclude robots.txt from localization

- Add 'robots.txt' to exclude_from_localization list
- Prevents language-specific copies of robots.txt (should stay single, root-level)

Rationale: ensure consistent crawl directives across all locales.

Author: yunseo-kim

_config.yml

@@ -179,7 +179,7 @@ baseurl: ""
 # Polyglot Settings
 languages: ["en", "ko", "ja", "zh-TW", "es", "pt-BR", "fr", "de"]
 default_lang: "en"
-exclude_from_localization: ["javascript", "images", "css", "public", "assets", "sitemap.xml"]
+exclude_from_localization: ["javascript", "images", "css", "public", "assets", "sitemap.xml", "robots.txt"]
 parallel_localization: true
 lang_from_path: true