feat: add GDPR cookie consent banner (#1216)

* feat: add GDPR cookie consent banner

Add a GDPR-compliant cookie consent banner that gates analytics (Google
Analytics) and functional cookies (comments) until user consent is given.

Features:
- Theme-consistent styling using CSS variables (light/dark mode)
- Settings panel with category toggles (necessary, analytics, functional)
- Consent stored in cookie for 365 days
- Google Analytics only loads after analytics consent
- Comments only load after functional consent
- Translations for all 32 supported languages
- Accessible with proper ARIA attributes and focus management

Configuration in hugo.yaml:
  params:
    cookies:
      enabled: true
      categories:
        analytics: true
        functional: true

When cookies.enabled is false, scripts load normally without consent gating.

Closes #412

* refactor: move consent-gated GA to cookies/analytics.html

Move Google Analytics consent logic to avoid shadowing Hugo's internal
`_internal/google_analytics.html` template.

Changes:
- Rename google_analytics.html → cookies/analytics.html
- Update head.html to conditionally load:
  - cookies.enabled=true: cookies/analytics.html (consent-gated)
  - cookies.enabled=false: Hugo's _internal/google_analytics.html
- Align cookies/analytics.html with Hugo's internal template:
  - Support Privacy.GoogleAnalytics.Disable setting
  - Support Privacy.GoogleAnalytics.RespectDoNotTrack setting
  - Add UA- prefix deprecation warning

Note: Custom JS is required for consent-gated GA because Hugo templates
render at build time, but consent happens at runtime. We cannot call
Hugo's internal template after the user grants consent - we must
dynamically inject the GA script via JavaScript.

* style: indent cookies/analytics.html

* refactor: don't use default, put default configurations in params.toml

* fix: don't use `description` as translation key because it's reserved and will throw error

* fix: remove footer/components/custom-font.html call

* fix: banner showSettings key

* style: indent comments/include

* Add missing article.alert translation back

* style: format i18n toml files

* style: indent head/head.html

* style adjustment

* style: add missing -

* style: format demo/config/params.toml

* style: remove redundant comments from cookies.scss

* style: update box-shadow for cookie banner content

---------

Co-authored-by: delize <4028612+delize@users.noreply.github.com>
Co-authored-by: Jimmy Cai <jimmy@cai.im>

i18n/fr.toml

@@ -52,3 +52,27 @@ darkMode   = "Mode sombre"
 [footer]
     builtWith  = "Généré avec {{ .Generator }}"
     designedBy = "Thème {{ .Theme }} conçu par {{ .DesignedBy }}"
+
+[cookies]
+    title             = "Consentement aux cookies"
+    text              = "Nous utilisons des cookies pour améliorer votre expérience de navigation et analyser le trafic du site."
+    acceptAll         = "Tout accepter"
+    deny              = "Refuser"
+    managePreferences = "Gérer les préférences"
+    settingsTitle     = "Préférences de cookies"
+    savePreferences   = "Enregistrer les préférences"
+    cancel            = "Annuler"
+    footerLink        = "Paramètres des cookies"
+    commentsDisabled  = "Les commentaires sont désactivés jusqu'à ce que vous acceptiez les cookies fonctionnels."
+
+    [cookies.necessary]
+        title = "Nécessaires"
+        text  = "Ces cookies sont nécessaires au fonctionnement du site et ne peuvent pas être désactivés."
+
+    [cookies.analytics]
+        title = "Analytiques"
+        text  = "Ces cookies nous aident à comprendre comment les visiteurs interagissent avec notre site."
+
+    [cookies.functional]
+        title = "Fonctionnels"
+        text  = "Ces cookies permettent des fonctionnalités comme les commentaires et le contenu intégré."