feat: major dependency upgrades, remove Redis, fix mongoose 9 types

Dependencies upgraded:
- svelte 5.38→5.55, @sveltejs/kit 2.37→2.56, adapter-node 5.3→5.5
- mongoose 8→9, sharp 0.33→0.34, typescript 5→6
- lucide-svelte → @lucide/svelte 1.7 (Svelte 5 native package)
- vite 7→8 with rolldown (build time 33s→14s)
- Removed terser (esbuild/oxc default minifier is 20-100x faster)

Infrastructure:
- Removed Redis/ioredis cache layer — MongoDB handles caching natively
- Deleted src/lib/server/cache.ts and all cache.get/set/invalidate usage
- Removed redis-cli from deploy workflow, Redis env vars from .env.example

Mongoose 9 migration:
- Replaced deprecated `new: true` with `returnDocument: 'after'` (16 files)
- Fixed strict query filter types for ObjectId/paymentId fields
- Fixed season param type (string→number) in recipe API
- Removed unused @ts-expect-error in WorkoutSession model

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

@@ -3,7 +3,6 @@ import { PaymentSplit } from '$models/PaymentSplit';
 import { Payment } from '$models/Payment'; // Need to import Payment for populate to work
 import { dbConnect } from '$utils/db';
 import { error, json } from '@sveltejs/kit';
-import cache from '$lib/server/cache';
 
 export const GET: RequestHandler = async ({ locals, url }) => {
   const auth = await locals.auth();
@@ -18,14 +17,6 @@ export const GET: RequestHandler = async ({ locals, url }) => {
 
   try {
     if (includeAll) {
-      // Try cache first for all balances
-      const cacheKey = 'cospend:balance:all';
-      const cached = await cache.get(cacheKey);
-
-      if (cached) {
-        return json(JSON.parse(cached));
-      }
-
       const allSplits = await PaymentSplit.aggregate([
         {
           $group: {
@@ -58,20 +49,9 @@ export const GET: RequestHandler = async ({ locals, url }) => {
         allBalances: allSplits
       };
 
-      // Cache for 30 minutes
-      await cache.set(cacheKey, JSON.stringify(result), 1800);
-
       return json(result);
 
     } else {
-      // Try cache first for individual user balance
-      const cacheKey = `cospend:balance:${username}`;
-      const cached = await cache.get(cacheKey);
-
-      if (cached) {
-        return json(JSON.parse(cached));
-      }
-
       const userSplits = await PaymentSplit.find({ username }).lean();
 
       // Calculate net balance: negative = you are owed money, positive = you owe money
@@ -112,9 +92,6 @@ export const GET: RequestHandler = async ({ locals, url }) => {
         recentSplits
       };
 
-      // Cache for 30 minutes
-      await cache.set(cacheKey, JSON.stringify(result), 1800);
-
       return json(result);
     }
 
@@ -122,4 +99,4 @@ export const GET: RequestHandler = async ({ locals, url }) => {
     console.error('Error calculating balance:', e);
     throw error(500, 'Failed to calculate balance');
   }
-};
+};