fix: implement persistent MongoDB connections and resolve race conditions

- Replace connect/disconnect pattern with persistent connection pool
- Add explicit database initialization on server startup
- Remove all dbDisconnect() calls from API endpoints to prevent race conditions
- Fix MongoNotConnectedError when scheduler runs concurrently with API requests
- Add connection pooling with proper MongoDB driver options
- Add safety check for recipes array in favorites utility

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/routes/api/rezepte/items/icon/+server.ts

@@ -1,12 +1,11 @@
 import { json, type RequestHandler } from '@sveltejs/kit';
 import { Recipe } from '../../../../../models/Recipe';
-import { dbConnect, dbDisconnect } from '../../../../../utils/db';
+import { dbConnect } from '../../../../../utils/db';
 import type {BriefRecipeType} from '../../../../../types/types';
 
 export const GET: RequestHandler = async ({params}) => {
   await dbConnect();
   let icons = (await Recipe.distinct('icon').lean());
-  await dbDisconnect();
 
   icons = JSON.parse(JSON.stringify(icons));
   return json(icons);

src/routes/api/rezepte/items/icon/[icon]/+server.ts

@@ -1,13 +1,12 @@
 import { json, type RequestHandler } from '@sveltejs/kit';
 import { Recipe } from '../../../../../../models/Recipe';
-import { dbConnect, dbDisconnect } from '../../../../../../utils/db';
+import { dbConnect } from '../../../../../../utils/db';
 import type {BriefRecipeType} from '../../../../../../types/types';
 import { rand_array } from '$lib/js/randomize';
 
 export const GET: RequestHandler = async ({params}) => {
   await dbConnect();
   let recipes = rand_array(await Recipe.find({icon: params.icon}, 'name short_name images tags category icon description season dateModified').lean()) as BriefRecipeType[];
-  await dbDisconnect();
 
   recipes = JSON.parse(JSON.stringify(recipes));
   return json(recipes);