fix: resolve all 1008 svelte-check type errors across codebase

Add type annotations, JSDoc types, null checks, and proper generics
to eliminate all svelte-check errors. Key changes include:
- Type $state(null) variables to avoid 'never' inference
- Add JSDoc typedefs for plain <script> components
- Fix mongoose model typing with Model<any> to avoid union complexity
- Add App.Error/App.PageState interfaces in app.d.ts
- Fix tuple types to array types in types.ts
- Type catch block errors and API handler params
- Add null safety for DOM queries and optional chaining
- Add standard line-clamp property alongside -webkit- prefix

src/lib/utils/settlements.ts

@@ -48,13 +48,13 @@ export function getSettlementReceiver(payment: any): string {
   }
   
   // Find the user who has a positive amount (the receiver)
-  const receiver = payment.splits.find(split => split.amount > 0);
+  const receiver = payment.splits.find((split: any) => split.amount > 0);
   if (receiver && receiver.username) {
     return receiver.username;
   }
   
   // Fallback: find the user who is not the payer
-  const otherUser = payment.splits.find(split => split.username !== payment.paidBy);
+  const otherUser = payment.splits.find((split: any) => split.username !== payment.paidBy);
   if (otherUser && otherUser.username) {
     return otherUser.username;
   }