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/cospend/settle/+page.svelte

@@ -5,21 +5,22 @@
   import { PREDEFINED_USERS, isPredefinedUsersMode } from '$lib/config/users';
 
 
-  import { formatCurrency } from '$lib/utils/formatters';  export let data;
-  export let form;
+  import { formatCurrency } from '$lib/utils/formatters';
+
+  let { data, form } = $props();
 
   // Use server-side data with progressive enhancement
-  let debtData = data.debtData || {
+  let debtData = $state(data.debtData || {
     whoOwesMe: [],
     whoIOwe: [],
     totalOwedToMe: 0,
     totalIOwe: 0
-  };
-  let loading = false; // Start as false since we have server data
-  let error = data.error || form?.error || null;
-  let selectedSettlement = null;
-  let settlementAmount = form?.values?.amount || '';
-  let submitting = false;
+  });
+  let loading = $state(false); // Start as false since we have server data
+  let error = $state(data.error || form?.error || null);
+  let selectedSettlement = $state(null);
+  let settlementAmount = $state(form?.values?.amount || '');
+  let submitting = $state(false);
   let predefinedMode = isPredefinedUsersMode();
 
   onMount(() => {