Add mobile overflow nav, law check feature, and favicon

Nav: "Fonctionnement" and "Flyer QR" restored on mobile via a ···
overflow dropdown (click-outside closes); other links always visible

Law check: new POST /api/check-law endpoint (5/min, 20/h) calls
mistral-small with a new LAW_CHECK_PROMPT to detect if a proposal is
already covered by French or EU law. Informational only, non-blocking.
Frontend: "Vérifier le cadre légal existant" button below textarea in
home.tsx; result displayed with Scale icon; resets on content change.

Favicon: replaced placeholder red square with a petrol rounded square
containing a serif "V" (for Voix) in warm cream — matches brand palette

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

artifacts/flask-api/app.py

@@ -52,7 +52,7 @@ from database import (
     get_consultation_contributions, delete_consultation,
     check_ip_blacklist, record_ip_rejection, get_ip_blacklist, remove_ip_blacklist,
 )
-from ai_agent import filter_idea, synthesize_ideas
+from ai_agent import filter_idea, synthesize_ideas, check_existing_law
 
 # ─── Logging ────────────────────────────────────────────────────────────────
 
@@ -1216,6 +1216,25 @@ def admin_delete_consultation(slug: str):
     return jsonify({"ok": True})
 
 
+@app.post("/api/check-law")
+@limiter.limit("5 per minute;20 per hour")
+def check_law_route():
+    """
+    Vérifie si une proposition est déjà couverte par une loi française ou européenne.
+    Endpoint public, rate-limité. Non bloquant — retourne une note informative.
+    """
+    if not request.is_json:
+        return jsonify({"error": "bad_request", "message": "Content-Type doit être application/json."}), 400
+    data = request.get_json(silent=True) or {}
+    content = sanitize_text(str(data.get("content", ""))).strip()
+    if not content or len(content) < 10:
+        return jsonify({"error": "validation_error", "message": "Contenu trop court."}), 400
+    if len(content) > 1000:
+        return jsonify({"error": "validation_error", "message": "Contenu trop long (max 1000 caractères)."}), 400
+    note = check_existing_law(content)
+    return jsonify({"note": note})
+
+
 @app.get("/api/admin/ip-blacklist")
 @require_admin
 def admin_list_ip_blacklist():