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/routes/api/cospend/debts/+server.ts

@@ -42,7 +42,7 @@ export const GET: RequestHandler = async ({ locals }) => {
       .lean();
 
     // Get all other users who have splits with payments involving the current user
-    const paymentIds = userSplits.map(split => split.paymentId._id);
+    const paymentIds = userSplits.map(split => (split.paymentId as any)._id);
     const allRelatedSplits = await PaymentSplit.find({
       paymentId: { $in: paymentIds },
       username: { $ne: currentUser }
@@ -60,7 +60,7 @@ export const GET: RequestHandler = async ({ locals }) => {
 
       // Find other participants in this payment
       const otherSplits = allRelatedSplits.filter(s =>
-        s.paymentId._id.toString() === split.paymentId._id.toString()
+        (s.paymentId as any)._id.toString() === (split.paymentId as any)._id.toString()
       );
 
       for (const otherSplit of otherSplits) {

src/routes/api/cospend/monthly-expenses/+server.ts

@@ -76,7 +76,7 @@ export const GET: RequestHandler = async ({ url, locals }) => {
       }
     ];
 
-    const results = await Payment.aggregate(pipeline);
+    const results = await Payment.aggregate(pipeline as any);
 
     // Transform data into chart-friendly format
     const monthsMap = new Map();
@@ -106,13 +106,13 @@ export const GET: RequestHandler = async ({ url, locals }) => {
 
     // Convert to arrays for Chart.js
     const allMonths = Array.from(monthsMap.keys()).sort();
-    const categoryList = Array.from(categories).sort();
+    const categoryList = Array.from(categories).sort() as string[];
 
     // Find the first month with any data and trim empty months from the start
     let firstMonthWithData = 0;
     for (let i = 0; i < allMonths.length; i++) {
       const monthData = monthsMap.get(allMonths[i]);
-      const hasData = Object.values(monthData).some(value => value > 0);
+      const hasData = Object.values(monthData).some((value: any) => value > 0);
       if (hasData) {
         firstMonthWithData = i;
         break;

src/routes/api/cospend/payments/+server.ts

@@ -102,7 +102,7 @@ export const POST: RequestHandler = async ({ request, locals }) => {
       exchangeRate = conversion.exchangeRate;
     } catch (e) {
       console.error('Currency conversion error:', e);
-      throw error(400, `Failed to convert ${inputCurrency} to CHF: ${e.message}`);
+      throw error(400, `Failed to convert ${inputCurrency} to CHF: ${e instanceof Error ? e.message : String(e)}`);
     }
   }
 
@@ -146,7 +146,7 @@ export const POST: RequestHandler = async ({ request, locals }) => {
       };
     });
 
-    const splitPromises = convertedSplits.map((split) => {
+    const splitPromises = convertedSplits.map((split: any) => {
       return PaymentSplit.create(split);
     });
 

src/routes/api/cospend/payments/[id]/+server.ts

@@ -36,7 +36,7 @@ export const GET: RequestHandler = async ({ params, locals }) => {
     await cache.set(cacheKey, JSON.stringify(result), 1800);
 
     return json(result);
-  } catch (e) {
+  } catch (e: any) {
     if (e.status === 404) throw e;
     throw error(500, 'Failed to fetch payment');
   } finally {
@@ -108,7 +108,7 @@ export const PUT: RequestHandler = async ({ params, request, locals }) => {
     await invalidateCospendCaches(allAffectedUsers, id);
 
     return json({ success: true, payment: updatedPayment });
-  } catch (e) {
+  } catch (e: any) {
     if (e.status) throw e;
     throw error(500, 'Failed to update payment');
   } finally {
@@ -148,7 +148,7 @@ export const DELETE: RequestHandler = async ({ params, locals }) => {
     await invalidateCospendCaches(affectedUsernames, id);
 
     return json({ success: true });
-  } catch (e) {
+  } catch (e: any) {
     if (e.status) throw e;
     throw error(500, 'Failed to delete payment');
   } finally {

src/routes/api/cospend/upload/+server.ts

@@ -55,7 +55,7 @@ export const POST: RequestHandler = async ({ request, locals }) => {
       path: publicPath
     });
 
-  } catch (err) {
+  } catch (err: any) {
     if (err.status) throw err;
     console.error('Upload error:', err);
     throw error(500, 'Failed to upload file');