Refactor cospend components and add SSR support to settle page

- Create reusable components: ImageUpload, FormSection, SplitMethodSelector, UsersList
- Replace duplicate code across add/edit pages with shared components
- Remove created-by info and edit/delete buttons from payments list
- Add server-side rendering support to settle page with form actions
- Fix settlement submission redirect issue
- Remove redundant back button from settle page

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

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

src/lib/components/FormSection.svelte

@@ -0,0 +1,38 @@
+<script>
+  export let title = '';
+</script>
+
+<div class="form-section">
+  {#if title}
+    <h2>{title}</h2>
+  {/if}
+  <slot />
+</div>
+
+<style>
+  .form-section {
+    background: var(--nord6);
+    padding: 1.5rem;
+    border-radius: 0.75rem;
+    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+    border: 1px solid var(--nord4);
+  }
+
+  .form-section h2 {
+    margin-top: 0;
+    margin-bottom: 1rem;
+    color: var(--nord0);
+    font-size: 1.25rem;
+  }
+
+  @media (prefers-color-scheme: dark) {
+    .form-section {
+      background: var(--nord1);
+      border-color: var(--nord2);
+    }
+
+    .form-section h2 {
+      color: var(--font-default-dark);
+    }
+  }
+</style>