feat: Improve search config + rename Dashboard + fix SearXNG

SearXNG:
- Fix tini not found error by calling entrypoint.sh directly
- Keep limiter.toml creation at container startup

UI Changes:
- Rename "Tableau de bord" to "Suivis produits" in navigation
- Move CSS selector configuration from item modal to Settings page
- Add price_selector field to search sites configuration
- Display CSS selector badge on site cards

Backend:
- Add price_selector column to SearchSite model and schemas
- Update init.sql with search_sites table and migration for existing DBs

frontend/src/i18n/locales/fr.json

@@ -4,14 +4,14 @@
         "tagline": "Suivi de prix intelligent"
     },
     "nav": {
-        "dashboard": "Tableau de bord",
+        "dashboard": "Suivis produits",
         "search": "Recherche",
         "settings": "Paramètres",
         "lightMode": "Mode clair",
         "darkMode": "Mode sombre"
     },
     "dashboard": {
-        "title": "Tableau de bord",
+        "title": "Suivis produits",
         "description": "Gérez vos articles suivis et surveillez les changements de prix.",
         "addItem": "Ajouter un article",
         "refreshAll": "Actualiser tout",