fix(views): make Restaurant JSON-safe before passing to Jinja

All four CMS pages (menu / orders / kds / settings) crashed with

    TypeError: JSONEncoder.default() missing 1 required positional
    argument: 'o'

because templates do `{{ restaurant | tojson | safe }}`. `tojson`
runs Python's stdlib `json.JSONEncoder` which can't serialize the
`datetime` on `Restaurant.time` (or any other datetime nested in
the model). The browser saw '500 / 'o'' (KeyError-flavored).

Pydantic v1's .json() handles datetime correctly (ISO 8601). New
helper _restaurant_jsonable rounds-trips the Restaurant via .json()
+ json.loads() and returns a fully JSON-safe dict, then all four
view handlers pass that instead of restaurant.dict().

views.py

@@ -15,6 +15,7 @@ Pages
 All pages require a logged-in LNbits user (check_user_exists).
 """
 
+import json
 from http import HTTPStatus
 
 from fastapi import APIRouter, Depends, Request
@@ -26,6 +27,7 @@ from lnbits.decorators import check_user_exists
 from lnbits.helpers import template_renderer
 
 from .crud import get_restaurant_by_slug
+from .models import Restaurant
 
 restaurant_generic_router = APIRouter()
 
@@ -34,6 +36,21 @@ def restaurant_renderer():
     return template_renderer(["restaurant/templates"])
 
 
+def _restaurant_jsonable(restaurant: Restaurant) -> dict:
+    """
+    Convert a Restaurant pydantic model to a plain JSON-serializable
+    dict for Jinja's `tojson` filter.
+
+    `restaurant.dict()` returns a dict with a `datetime` on `time`,
+    which Python's stdlib `JSONEncoder` (used by Jinja `tojson`) can't
+    serialize — it errors out as
+        TypeError: JSONEncoder.default() missing 1 required positional argument: 'o'
+    Pydantic v1's `.json()` knows how to serialize datetime as
+    ISO-8601, so we round-trip via JSON to get a clean dict.
+    """
+    return json.loads(restaurant.json())
+
+
 @restaurant_generic_router.get("/", response_class=HTMLResponse)
 async def index(request: Request, user: User = Depends(check_user_exists)):
     return restaurant_renderer().TemplateResponse(
@@ -56,7 +73,7 @@ async def menu_builder(
         {
             "request": request,
             "user": user.json(),
-            "restaurant": restaurant.dict(),
+            "restaurant": _restaurant_jsonable(restaurant),
         },
     )
 
@@ -75,7 +92,7 @@ async def orders(
         {
             "request": request,
             "user": user.json(),
-            "restaurant": restaurant.dict(),
+            "restaurant": _restaurant_jsonable(restaurant),
         },
     )
 
@@ -94,7 +111,7 @@ async def kds(
         {
             "request": request,
             "user": user.json(),
-            "restaurant": restaurant.dict(),
+            "restaurant": _restaurant_jsonable(restaurant),
         },
     )
 
@@ -113,6 +130,6 @@ async def settings_page(
         {
             "request": request,
             "user": user.json(),
-            "restaurant": restaurant.dict(),
+            "restaurant": _restaurant_jsonable(restaurant),
         },
     )