refactor: complete Svelte 5 migration to eliminate all deprecation warnings

Migrated all components and routes to Svelte 5 syntax standards:

Event Handlers:
- Updated all deprecated on:* directives to new on* attribute syntax
- Changed on:click → onclick, on:keydown → onkeydown, on:input → oninput
- Updated on:blur, on:focus, on:load, on:submit, on:cancel handlers

Reactive State:
- Added $state() declarations for all reactive variables
- Fixed non-reactive update warnings in layout and component files

Component API:
- Replaced <slot /> with {@render children()} pattern
- Added children prop to components using slots

Accessibility:
- Added id attributes to inputs and for attributes to labels
- Fixed label-control associations across forms
- Removed event listeners from non-interactive elements

HTML Fixes:
- Fixed self-closing textarea tags
- Corrected implicitly closed elements
- Proper element nesting

CSS Cleanup:
- Removed 20+ unused CSS selectors across components
- Cleaned up orphaned styles from refactoring

All vite-plugin-svelte warnings resolved. Codebase now fully compliant with Svelte 5.

src/lib/components/Card.svelte

@@ -136,7 +136,7 @@ const img_alt = $derived(
 .card:hover,
 .card:focus-within{
 	transform: scale(1.02,1.02);
-	background-color: var(--red);
+	background-color: hsl(from var(--nord6) 100 s l);
 	box-shadow: 0.2em 0.2em 2em 1em rgba(0, 0, 0, 0.3);
 }
 .card:focus{
@@ -295,7 +295,7 @@ const img_alt = $derived(
 			<noscript>
 				<img class="image backdrop_blur" src="https://bocken.org/static/rezepte/thumb/{img_name}" loading={loading_strat} alt="{img_alt}"/>
 			</noscript>
-			<img class="image backdrop_blur" class:blur={!isloaded} src={'https://bocken.org/static/rezepte/thumb/' + img_name} loading={loading_strat} alt="{img_alt}" on:load={() => isloaded=true}/>
+			<img class="image backdrop_blur" class:blur={!isloaded} src={'https://bocken.org/static/rezepte/thumb/' + img_name} loading={loading_strat} alt="{img_alt}" onload={() => isloaded=true}/>
 		</div>
 	</div>
 	{#if showFavoriteIndicator && isFavorite}