feat: add favicon, structured data & SEO optimization for Google sitelinks

- Add SVG favicon (H logo navy+orange) for all sizes (32, 180, 192, 512)
- Add web manifest (site.webmanifest) for PWA compatibility
- Add theme-color meta tag (#1B2A4A navy)
- Add 3 structured data schemas: LocalBusiness, WebSite, SiteNavigationElement
- WebSite schema enables Google to show site name + search box
- SiteNavigationElement signals main pages for sitelinks display
- Add canonical URLs to all pages (macon, paysagiste, plombier, legal pages)
- Add metadata to pages missing it (mentions-legales, confidentialite, cgv)
- Add candidature/layout.tsx for metadata on client component page
- Optimize sitemap with consistent BASE_URL and candidature/cgv pages
- Add telephone, email, opening hours to LocalBusiness schema

https://claude.ai/code/session_01V8YAjpqRQ3bfBYsABYsEgo

public/site.webmanifest

@@ -0,0 +1,21 @@
+{
+  "name": "HookLab - Sites web pour artisans du Nord",
+  "short_name": "HookLab",
+  "description": "Création de sites internet et référencement Google pour artisans du bâtiment dans le Nord (59).",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#F7F8FA",
+  "theme_color": "#1B2A4A",
+  "icons": [
+    {
+      "src": "/icon-192.svg",
+      "sizes": "192x192",
+      "type": "image/svg+xml"
+    },
+    {
+      "src": "/icon-512.svg",
+      "sizes": "512x512",
+      "type": "image/svg+xml"
+    }
+  ]
+}