Code maintainability fixes

server/prisma/schema.prisma

@@ -7,7 +7,6 @@ generator client {
 
 datasource db {
   provider = "sqlite"
-  url      = env("DATABASE_URL")
 }
 
 model User {
@@ -60,6 +59,7 @@ model Exercise {
   isUnilateral         Boolean  @default(false)
   
   sets                 WorkoutSet[]
+  planExercises        PlanExercise[]
 }
 
 model WorkoutSession {
@@ -102,8 +102,19 @@ model WorkoutPlan {
   user        User     @relation(fields: [userId], references: [id], onDelete: Cascade)
   name        String
   description String?
-  exercises   String   // JSON string of exercise IDs
+  exercises   String?  // JSON string of exercise IDs (Deprecated, to be removed)
+  planExercises PlanExercise[]
   createdAt   DateTime @default(now())
   updatedAt   DateTime @updatedAt
 }
 
+model PlanExercise {
+  id           String      @id @default(uuid())
+  planId       String
+  plan         WorkoutPlan @relation(fields: [planId], references: [id], onDelete: Cascade)
+  exerciseId   String
+  exercise     Exercise    @relation(fields: [exerciseId], references: [id])
+  order        Int
+  isWeighted   Boolean     @default(false)
+}
+