SEO : comble les régressions de la migration Astro → SvelteKit

- composant Seo.svelte partagé : canonical, Open Graph complet
  (type, url, title, description, image, locale fr_FR, site_name)
  et Twitter Cards sur toutes les pages
- branché sur l'accueil, /outils, /quiz, /contribuer et les fiches
  outils (les meta OG en dur des fiches sont remplacés par le
  composant, JSON-LD conservé)
- script prebuild gen-sitemap.mjs : régénère static/sitemap.xml
  (59 URLs, slugs relus depuis content/outils/) — remplace le
  sitemap qu'apportait @astrojs/sitemap
- robots.txt référence le sitemap en URL absolue

frontend/src/lib/components/Seo.svelte

@@ -0,0 +1,43 @@
+<script lang="ts">
+  import { t } from '$lib/i18n/index.svelte'
+  import { SITE_URL } from '$lib/site'
+
+  interface Props {
+    /** titre court de la page (« Annuaire des outils ») — omis sur l'accueil */
+    title?: string
+    description: string
+    /** chemin canonique avec slash final, ex. `/outils/` (trailingSlash: 'always') */
+    path: string
+    type?: 'website' | 'article'
+  }
+
+  let { title, description, path, type = 'website' }: Props = $props()
+
+  // même format que l'ère actuelle : « Titre — Lagé Chat Control »,
+  // et « Lagé Chat Control — accroche » sur l'accueil
+  let fullTitle = $derived(title ? `${title} — ${t('site.name')}` : `${t('site.name')} — ${t('site.tagline')}`)
+  let url = $derived(`${SITE_URL}${path}`)
+  // favicon.png servi en og:image — réellement 192×192 (vérifié au build)
+  const image = `${SITE_URL}/favicon.png`
+</script>
+
+<svelte:head>
+  <title>{fullTitle}</title>
+  <meta name="description" content={description} />
+  <link rel="canonical" href={url} />
+  <meta property="og:type" content={type} />
+  <meta property="og:url" content={url} />
+  <meta property="og:title" content={fullTitle} />
+  <meta property="og:description" content={description} />
+  <meta property="og:image" content={image} />
+  <meta property="og:image:width" content="192" />
+  <meta property="og:image:height" content="192" />
+  <meta property="og:image:alt" content={t('site.name')} />
+  <meta property="og:locale" content="fr_FR" />
+  <meta property="og:site_name" content={t('site.name')} />
+  <meta name="twitter:card" content="summary" />
+  <meta name="twitter:title" content={fullTitle} />
+  <meta name="twitter:description" content={description} />
+  <meta name="twitter:image" content={image} />
+</svelte:head>
+

frontend/src/lib/site.ts

@@ -1,5 +1,8 @@
 /** Constantes du site — un seul endroit à changer si la forge bouge. */
 export const REPO_URL = 'https://labola.o-k-i.net/cyber-mawonaj/lage-chat-control'
+
+/** Origine de production — base des URL absolues SEO (canonical, OG, sitemap). */
+export const SITE_URL = 'https://chatcontrol.o-k-i.net'
 export const NEW_TOOL_ISSUE_URL = `${REPO_URL}/issues/new?template=.gitea/ISSUE_TEMPLATE/nouvo-zouti.yaml`
 
 /**

frontend/src/routes/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import { base } from '$app/paths'
+  import Seo from '$lib/components/Seo.svelte'
   import ToolCard from '$lib/components/ToolCard.svelte'
   import { adoptedCount } from '$lib/adopted.svelte'
   import { t } from '$lib/i18n/index.svelte'
@@ -10,10 +11,7 @@
   let jes = $derived(adoptedCount())
 </script>
 
-<svelte:head>
-  <title>{t('site.name')} — {t('site.tagline')}</title>
-  <meta name="description" content={t('site.description')} />
-</svelte:head>
+<Seo description={t('site.description')} path="/" />
 
 <!-- Valeur livrée en < 5 s (doctrine §2.1) : le héros dit quoi, pour qui,
      et donne UNE action primaire (Von Restorff, doctrine §1.2). -->

frontend/src/routes/contribuer/+page.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import Seo from '$lib/components/Seo.svelte'
   import { t } from '$lib/i18n/index.svelte'
   import { NEW_TOOL_ISSUE_URL, REPO_URL } from '$lib/site'
 
@@ -10,10 +11,7 @@
   ] as const
 </script>
 
-<svelte:head>
-  <title>{t('contrib.title')} — {t('site.name')}</title>
-  <meta name="description" content={t('contrib.intro')} />
-</svelte:head>
+<Seo title={t('contrib.title')} description={t('contrib.intro')} path="/contribuer/" />
 
 <header class="stack">
   <h1>{t('contrib.title')}</h1>

frontend/src/routes/outils/+page.svelte

@@ -7,6 +7,7 @@
   import ToolCard from '$lib/components/ToolCard.svelte'
   import EndMarker from '$lib/components/EndMarker.svelte'
   import DifficultyBadge from '$lib/components/DifficultyBadge.svelte'
+  import Seo from '$lib/components/Seo.svelte'
   import { t } from '$lib/i18n/index.svelte'
 
   let { data } = $props()
@@ -43,10 +44,7 @@
   }
 </script>
 
-<svelte:head>
-  <title>{t('directory.title')} — {t('site.name')}</title>
-  <meta name="description" content={t('directory.intro')} />
-</svelte:head>
+<Seo title={t('directory.title')} description={t('directory.intro')} path="/outils/" />
 
 <header class="stack">
   <h1>{t('directory.title')}</h1>

frontend/src/routes/outils/[slug]/+page.svelte

@@ -2,6 +2,7 @@
   import { base } from '$app/paths'
   import AdoptButton from '$lib/components/AdoptButton.svelte'
   import DifficultyBadge from '$lib/components/DifficultyBadge.svelte'
+  import Seo from '$lib/components/Seo.svelte'
   import { getLocale, t } from '$lib/i18n/index.svelte'
 
   let { data } = $props()
@@ -34,15 +35,12 @@
 </script>
 
 <svelte:head>
-  <title>{tool.name} — {t('site.name')}</title>
-  <meta name="description" content={tool.excerpt} />
-  <meta property="og:title" content={tool.name} />
-  <meta property="og:description" content={tool.excerpt} />
-  <meta property="og:type" content="article" />
   <!-- eslint-disable-next-line svelte/no-at-html-tags — JSON-LD généré au build depuis nos propres données -->
   {@html jsonLd}
 </svelte:head>
 
+<Seo title={tool.name} description={tool.excerpt} path="/outils/{tool.slug}/" type="article" />
+
 <nav aria-label={t('tool.backToDirectory')}>
   <a href="{base}/outils">← {t('tool.backToDirectory')}</a>
 </nav>

frontend/src/routes/quiz/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import { base } from '$app/paths'
+  import Seo from '$lib/components/Seo.svelte'
   import { t } from '$lib/i18n/index.svelte'
   import type { QuizContent } from '$lib/content/quiz.server'
 
@@ -108,10 +109,7 @@
   }
 </script>
 
-<svelte:head>
-  <title>{t('quiz.title')} — {t('site.name')}</title>
-  <meta name="description" content={t('quiz.lede')} />
-</svelte:head>
+<Seo title={t('quiz.title')} description={t('quiz.lede')} path="/quiz/" />
 
 <header class="stack">
   <p class="eyebrow">{t('quiz.eyebrow')}</p>