Add complete settlement system with visual distinction

- Add settlement category with handshake emoji (🤝)
- Create settlement page for recording debt payments with user → user flow
- Implement settlement detection and visual styling across all views
- Add conditional "Settle Debts" button (hidden when balance is 0)
- Style settlement payments distinctly in recent activity with large profile pictures
- Add settlement flow styling in payments overview with green theme
- Update backend validation and Mongoose schema for settlement category
- Fix settlement receiver detection with proper user flow logic

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

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

src/routes/cospend/settle/+page.server.ts

@@ -0,0 +1,13 @@
+import type { PageServerLoad } from './$types';
+import { redirect } from '@sveltejs/kit';
+
+export const load: PageServerLoad = async ({ locals }) => {
+  const auth = await locals.auth();
+  if (!auth || !auth.user) {
+    throw redirect(302, '/login');
+  }
+
+  return {
+    session: auth
+  };
+};