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/routes/[recipeLang=recipeLang]/category/+page.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
     import type { PageData } from './$types';
     import "$lib/css/nordtheme.css";
-    let { data }: { data: PageData } = $props();
+    let { data } = $props<{ data: PageData }>();
     import TagCloud from '$lib/components/TagCloud.svelte';
     import TagBall from '$lib/components/TagBall.svelte';