Improve UI components and styling consistency

- Make AddButton component generic with href prop instead of hardcoded path
- Update PaymentModal with Nord theme styling and improved UX
- Add EditButton functionality to PaymentModal
- Remove old recurring payment add pages that are no longer needed
- Update all AddButton usages across rezepte and cospend pages
- Add AddButton to cospend dashboard for better navigation

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/components/AddButton.svelte

@@ -1,6 +1,8 @@
 <script lang='ts'>
 import ActionButton from "./ActionButton.svelte";
+
+export let href: string;
 </script>
-<ActionButton href="/rezepte/add">
+<ActionButton {href}>
 <svg class=icon_svg xmlns="http://www.w3.org/2000/svg" height="1em" viewBox="0 0 448 512"><!--! Font Awesome Free 6.4.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license (Commercial License) Copyright 2023 Fonticons, Inc. --><path d="M256 80c0-17.7-14.3-32-32-32s-32 14.3-32 32V224H48c-17.7 0-32 14.3-32 32s14.3 32 32 32H192V432c0 17.7 14.3 32 32 32s32-14.3 32-32V288H400c17.7 0 32-14.3 32-32s-14.3-32-32-32H256V80z"/></svg>
 </ActionButton>