feat: complete Svelte 5 migration across entire application

Migrated all components and routes from Svelte 4 to Svelte 5 syntax:

- Converted export let → $props() with generic type syntax
- Replaced createEventDispatcher → callback props
- Migrated $: reactive statements → $derived() and $effect()
- Updated two-way bindings with $bindable()
- Fixed TypeScript syntax: added lang="ts" to script tags
- Converted inline type annotations to generic parameter syntax

- Updated deprecated event directives to Svelte 5 syntax:
  - on:click → onclick
  - on:submit → onsubmit
  - on:change → onchange

- Converted deprecated <slot> elements → {@render children()}
- Updated slot props to Snippet types
- Fixed season/icon selector components with {#snippet} blocks

- Fixed non-reactive state by converting let → $state()
- Fixed infinite loop in EnhancedBalance by converting $effect → $derived
- Fixed Chart.js integration by converting $state proxies to plain arrays
- Updated cospend dashboard and payment pages with proper reactivity

- Migrated 20+ route files from export let data → $props()
- Fixed TypeScript type annotations in page components
- Updated reactive statements in error and cospend routes

- Removed invalid onchange attribute from Toggle component
- Fixed modal ID isolation in CreateIngredientList/CreateStepList
- Fixed dark mode button visibility in TranslationApproval
- Build now succeeds with zero deprecation warnings

All functionality tested and working. No breaking changes to user experience.

src/lib/components/FavoriteButton.svelte

@@ -1,12 +1,10 @@
 <script lang="ts">
   import { browser } from '$app/environment';
   import { enhance } from '$app/forms';
-  
-  export let recipeId: string;
-  export let isFavorite: boolean = false;
-  export let isLoggedIn: boolean = false;
-  
-  let isLoading = false;
+
+  let { recipeId, isFavorite = $bindable(false), isLoggedIn = false } = $props<{ recipeId: string, isFavorite?: boolean, isLoggedIn?: boolean }>();
+
+  let isLoading = $state(false);
 
   async function toggleFavorite(event: Event) {
     // If JavaScript is available, prevent form submission and handle client-side
@@ -71,7 +69,7 @@
       type="submit"
       class="favorite-button"
       disabled={isLoading}
-      on:click={toggleFavorite}
+      onclick={toggleFavorite}
       title={isFavorite ? 'Favorit entfernen' : 'Als Favorit speichern'}
     >
       {isFavorite ? '❤️' : '🖤'}