Typo Plus Jakarta Sans + renommage libreDecision + mode démo prod + seed mandats

- Fonte : Nunito → Plus Jakarta Sans (moderne, ronde sans être toy)
- Logo : ğ(Decision) → libreDecision (libre italic/muted + Decision bold)
- Footer et watermark DocumentPreview mis à jour
- Mode démo : DEMO_MODE flag dans config.py + auth.py (profils rapides en prod)
- docker-compose : ENVIRONMENT=production explicite + DEMO_MODE=true par défaut
- Seed : +décision Licence G1 v0.4.0, +3 mandats (ComTech, Admin Forgerons, Modération)
  runner 7→10 étapes, import Mandate/MandateStep ajouté

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

backend/app/routers/auth.py

@@ -147,7 +147,7 @@ async def verify_challenge(
 
     # 6. Get or create identity (apply dev profile if available)
     dev_profile = None
-    if settings.ENVIRONMENT == "development":
+    if settings.ENVIRONMENT == "development" or settings.DEMO_MODE:
         dev_profile = next((p for p in DEV_PROFILES if p["address"] == payload.address), None)
     identity = await get_or_create_identity(db, payload.address, dev_profile=dev_profile)
 
@@ -162,8 +162,8 @@ async def verify_challenge(
 
 @router.get("/dev/profiles")
 async def list_dev_profiles():
-    """List available dev profiles for quick login. Only available in development."""
-    if settings.ENVIRONMENT != "development":
+    """List available demo profiles for quick login. Available in development or demo mode."""
+    if settings.ENVIRONMENT != "development" and not settings.DEMO_MODE:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Not available")
     return DEV_PROFILES