feat: /sync settings page with price multiplier and description postfix

Adds price_multiplier and description_postfix to SyncConfig. The sync
page at /sync lets users configure them. vk_sync reads these per-user
settings and applies the multiplier to price and appends the postfix
as "(postfix)" to the VK product description.

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

web/routes/sync.py

@@ -0,0 +1,75 @@
+"""Sync settings page."""
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, Depends, Request
+from fastapi.responses import RedirectResponse
+
+from sqlalchemy.orm import Session
+
+from web.auth.session import get_current_user
+from web.config import settings
+from web.database import get_db
+from web.models.connections import SyncConfig
+from web.templates_env import templates
+
+router = APIRouter()
+
+
+def _render(request: Request, ctx: dict):
+    ctx["request"] = request
+    ctx.setdefault("jivosite_widget_id", settings.JIVOSITE_WIDGET_ID)
+    return templates.TemplateResponse(ctx.pop("request"), "sync.html", ctx)
+
+
+def _now():
+    return datetime.now(timezone.utc).replace(tzinfo=None)
+
+
+@router.get("/sync")
+async def sync_get(request: Request, db: Session = Depends(get_db)):
+    try:
+        user = get_current_user(request, db)
+    except Exception:
+        return RedirectResponse("/login", 303)
+
+    config = db.query(SyncConfig).filter_by(user_id=user.id).first()
+    return _render(request, {
+        "user": user,
+        "config": config,
+        "saved": request.query_params.get("saved"),
+    })
+
+
+@router.post("/sync/settings")
+async def sync_settings_post(request: Request, db: Session = Depends(get_db)):
+    try:
+        user = get_current_user(request, db)
+    except Exception:
+        return RedirectResponse("/login", 303)
+
+    form = await request.form()
+    raw_multiplier = str(form.get("price_multiplier", "1")).strip()
+    postfix = str(form.get("description_postfix", "")).strip() or None
+
+    try:
+        multiplier = float(raw_multiplier)
+        if multiplier <= 0:
+            raise ValueError
+    except ValueError:
+        multiplier = 1.0
+
+    config = db.query(SyncConfig).filter_by(user_id=user.id).first()
+    if config:
+        config.price_multiplier = multiplier
+        config.description_postfix = postfix
+    else:
+        config = SyncConfig(
+            user_id=user.id,
+            is_enabled=False,
+            price_multiplier=multiplier,
+            description_postfix=postfix,
+        )
+        db.add(config)
+
+    db.commit()
+    return RedirectResponse("/sync?saved=1", 303)