feat(hugo): replace deprecated APIs for Hugo v0.156+ compatibility

Migrate site.Data → hugo.Data (42 occurrences), site.IsMultiLingual →
hugo.IsMultilingual, and site.AllPages → hugo.Sites nested range.
Simplify Netlify redirects template to use pre-processed aliases
instead of relLangURL per gohugoio/hugo#14408.

modules/slides/layouts/slides/baseof.html

@@ -5,7 +5,7 @@
 
 <!doctype html>
 {{- $language_code := site.LanguageCode | default "en-us" -}}
-<html lang="{{$language_code}}" {{ if in site.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}
+<html lang="{{$language_code}}" {{ if in hugo.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}
       data-wc-theme-default="{{ (lower site.Params.hugoblox.theme.mode) | default "system" }}"
       data-hbb-relurl="{{ "" | relURL }}">
 

modules/slides/layouts/slides/baseof.present.html

@@ -22,7 +22,7 @@
 
 <!doctype html>
 {{- $language_code := site.LanguageCode | default "en-us" -}}
-<html lang="{{$language_code}}" {{ if in site.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}>
+<html lang="{{$language_code}}" {{ if in hugo.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}>
 <head>
 
   {{/* Asset versions */}}
@@ -33,7 +33,7 @@
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
-  <meta name="generator" content="HugoBlox Kit {{with site.Data.hugoblox.version}}{{.}}{{end}}">
+  <meta name="generator" content="HugoBlox Kit {{with hugo.Data.hugoblox.version}}{{.}}{{end}}">
 
   {{ with site.Home.OutputFormats.Get "WebAppManifest" }}
     <link rel="manifest" href="{{ .RelPermalink }}">