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/favicon.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" width="32" height="32">
+  <rect width="32" height="32" rx="6" fill="#1B2A4A"/>
+  <text x="16" y="23" text-anchor="middle" font-family="Inter, Arial, sans-serif" font-weight="800" font-size="20" fill="#FFFFFF">H</text>
+  <rect x="18" y="7" width="4" height="4" rx="1" fill="#E8772E"/>
+</svg>