fix: SSE 认证 + 收藏去重 + 数据库索引和级联删除

- #7: SSE events 接口校验 userId 房间成员身份，start() 加 try/catch
- #9: Favorite 新增 restaurantId 字段做精确去重，不再用 JSON contains
- #10: 补齐 Decision/Favorite/Room/BlindBoxIdea 缺失索引
- #11: Decision/Favorite/BlindBoxMember/BlindBoxIdea 加 onDelete Cascade

prisma/schema.prisma

@@ -12,6 +12,8 @@ model Room {
   data      String
   createdAt DateTime @default(now())
   expiresAt DateTime
+
+  @@index([expiresAt])
 }
 
 model User {
@@ -40,15 +42,22 @@ model Decision {
   matchType      String
   participants   Int
   createdAt      DateTime @default(now())
-  user           User     @relation(fields: [userId], references: [id])
+  user           User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@index([userId])
+  @@index([roomId])
 }
 
 model Favorite {
   id             String   @id @default(cuid())
   userId         String
+  restaurantId   String   @default("")
   restaurantData String
   createdAt      DateTime @default(now())
-  user           User     @relation(fields: [userId], references: [id])
+  user           User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([userId, restaurantId])
+  @@index([userId])
 }
 
 model BlindBoxRoom {
@@ -70,7 +79,7 @@ model BlindBoxMember {
   joinedAt DateTime @default(now())
 
   room BlindBoxRoom @relation(fields: [roomId], references: [id], onDelete: Cascade)
-  user User         @relation(fields: [userId], references: [id])
+  user User         @relation(fields: [userId], references: [id], onDelete: Cascade)
 
   @@unique([roomId, userId])
 }
@@ -85,6 +94,9 @@ model BlindBoxIdea {
   createdAt DateTime @default(now())
 
   room    BlindBoxRoom @relation(fields: [roomId], references: [id], onDelete: Cascade)
-  user    User         @relation("IdeaSubmitter", fields: [userId], references: [id])
-  drawnBy User?        @relation("IdeaDrawer", fields: [drawnById], references: [id])
+  user    User         @relation("IdeaSubmitter", fields: [userId], references: [id], onDelete: Cascade)
+  drawnBy User?        @relation("IdeaDrawer", fields: [drawnById], references: [id], onDelete: SetNull)
+
+  @@index([roomId, status])
+  @@index([userId])
 }