feat: add initial backend and frontend structure with models, DTOs, and WebSocket events

apps/backend/prisma/models/vectorMemory.prisma

@@ -0,0 +1,29 @@
+// Vector memory for embeddings (conversation and character knowledge)
+
+enum MemoryType {
+  conversation
+  character
+}
+
+model VectorMemory {
+  id              String    @id @default(uuid())
+  content         String
+  embedding       Unsupported("vector")?
+  memoryType      MemoryType @default(conversation)
+  metadata        Json?
+  createdAt       DateTime  @default(now())
+
+  conversationId  String?
+  conversation    Conversation? @relation(fields: [conversationId], references: [id], onDelete: Cascade)
+  
+  characterId     String?
+  character       Character?    @relation(fields: [characterId], references: [id], onDelete: Cascade)
+  
+  knowledgeId     String?
+  knowledge       CharacterKnowledge? @relation(fields: [knowledgeId], references: [id], onDelete: Cascade)
+
+  @@index([conversationId])
+  @@index([characterId])
+  @@index([knowledgeId])
+  @@index([memoryType])
+}