fix: migrate deprecated Hugo v0.158.0 language API

Replace deprecated config keys and template methods per Hugo v0.158.0:

Config (10 files):
- languageCode → locale
- languageName → label

Templates:
- site.LanguageCode → site.Language.Locale (baseof.html, head.html, schema.html x2)
- site.Language.Lang → site.Language.Name (single.html)
- .Lang → .Language.Name (likes.html, views.html)

Ref: https://discourse.gohugo.io/t/deprecations-in-v0-158-0/56869

layouts/partials/schema.html

@@ -6,7 +6,7 @@
     "@id": {{ site.Home.Permalink | safeURL }},
     "name": "{{ .Site.Title | safeJS }}",
     {{ with .Site.Params.description }}"description": "{{ . | safeJS }}",{{ end }}
-    {{ with .Site.LanguageCode }}"inLanguage": "{{ . }}",{{ end }}
+    {{ with .Site.Language.Locale }}"inLanguage": "{{ . }}",{{ end }}
     "url": {{ site.Home.Permalink | safeURL }},
     {{ with .Site.Params.keywords }}"keywords": {{ . }},{{ end }}
     "publisher" : {
@@ -25,7 +25,7 @@
     "name": "{{ .Title | safeJS }}",
     "headline": "{{ .Title | safeJS }}",
     {{ with .Description }}"description": "{{ . | safeJS }}",{{ end }}
-    {{ with .Site.LanguageCode }}"inLanguage": "{{ . }}",{{ end }}
+    {{ with .Site.Language.Locale }}"inLanguage": "{{ . }}",{{ end }}
     "url" : {{ .Permalink }},
     "author" : {
       "@type": "Person",