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/IconLayout.svelte

@@ -1,13 +1,26 @@
 <script lang="ts">
+    import type { Snippet } from 'svelte';
     import '$lib/css/nordtheme.css';
     import Recipes from '$lib/components/Recipes.svelte';
     import Search from './Search.svelte';
-    export let icons
-    export let active_icon
-    export let routePrefix = '/rezepte'
-    export let lang = 'de'
-    export let recipes = []
-    export let onSearchResults = (ids, categories) => {}
+
+    let {
+        icons,
+        active_icon,
+        routePrefix = '/rezepte',
+        lang = 'de',
+        recipes = [],
+        onSearchResults = (ids, categories) => {},
+        recipesSlot
+    }: {
+        icons: string[],
+        active_icon: string,
+        routePrefix?: string,
+        lang?: string,
+        recipes?: any[],
+        onSearchResults?: (ids: any[], categories: any[]) => void,
+        recipesSlot?: Snippet
+    } = $props();
 </script>
 
 <style>
@@ -79,5 +92,5 @@
 <Search icon={active_icon} {lang} {recipes} {onSearchResults}></Search>
 </section>
 <section>
-<slot name=recipes></slot>
+{@render recipesSlot?.()}
 </section>