Add Jivosite live chat widget support

Resolves #3 — widget is loaded on every page via base.html when
JIVOSITE_WIDGET_ID env var is set. Centralized Jinja2Templates instance
in web/templates_env.py with jivosite_widget_id as a global.

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

web/routes/evotor.py

@@ -4,7 +4,7 @@ import httpx
 from datetime import datetime
 from fastapi import APIRouter, Request, Depends, HTTPException
 from fastapi.responses import RedirectResponse, JSONResponse
-from fastapi.templating import Jinja2Templates
+from web.templates_env import templates
 from pydantic import BaseModel
 from sqlalchemy.orm import Session
 
@@ -16,7 +16,6 @@ from web.models import User, EvotorConnection
 logger = logging.getLogger(__name__)
 
 router = APIRouter(prefix="/evotor")
-templates = Jinja2Templates(directory="web/templates")
 
 EVOTOR_APP_URL = "https://market.evotor.ru/store/apps/{app_id}"
 EVOTOR_STORES_URL = "https://api.evotor.ru/stores"