feat: 完成 E 群組 — 關係子系統

- RelationshipService：E-1 未知對象自動建檔（禮貌+防備＝intimacy/trust=0）、
  E-3 親密度五階分層＋跨階事件（@nestjs/event-emitter，StageChangeLogService 獨立訂閱）、
  E-4 久未互動時親密度半衰期衰減並標記「久未見」
- SentimentLedgerService：E-2 關係帳本，負向事件套用放大係數，驗證同等級正負事件淨值為負
- IntentInterpreterService：E-6 依親密度將同一句模稜兩可的話解讀為玩笑或冒犯
- KeywordMemoryRetriever（C-6）擴充 E-5：新增 relatedUserId 加權，retrieve() 簽名改為接受 options 物件
- schema 新增 EpisodicMemory.relatedUserId，並補上所有子表對父表的 onDelete: Cascade/SetNull
  （E-2 測試時發現先前 B 群組遺漏這些規則會導致刪除關係時外鍵違反）
- apps/api 新增 /relationships/* 端點作為引擎驗證介面
- scripts/smoke/E.mjs：涵蓋 E-1~E-6 全部驗收情境

npm run restart && npm run smoke -- E 皆通過（E-V），A/B/C/D 群組冒煙測試無回歸。

本次另排除一個本機環境限定的 Prisma CLI 網路 checkpoint 卡住問題，並從一次部分套用的
migration 中手動恢復資料庫一致性（過程記錄於 todo.md 實作記錄，供後續群組參考）。

prisma/schema.prisma

@@ -50,7 +50,8 @@ model User {
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
 
-  relationships Relationship[]
+  relationships   Relationship[]
+  relatedMemories EpisodicMemory[]
 
   @@map("users")
 }
@@ -72,7 +73,7 @@ model Work {
 model Character {
   id     String  @id @default(cuid())
   workId String?
-  work   Work?   @relation(fields: [workId], references: [id])
+  work   Work?   @relation(fields: [workId], references: [id], onDelete: SetNull)
 
   source      CharacterSource
   buildStatus CharacterBuildStatus @default(CANDIDATE)
@@ -102,7 +103,7 @@ model Character {
 model CharacterAlias {
   id             String    @id @default(cuid())
   characterId    String
-  character      Character @relation(fields: [characterId], references: [id])
+  character      Character @relation(fields: [characterId], references: [id], onDelete: Cascade)
   formalName     String // 正式名
   nickname       String? // 暱稱
   calledByOthers String? // 他人稱呼（作品中其他角色如何稱呼）
@@ -114,7 +115,7 @@ model CharacterAlias {
 model EpisodicMemory {
   id               String       @id @default(cuid())
   characterId      String
-  character        Character    @relation(fields: [characterId], references: [id])
+  character        Character    @relation(fields: [characterId], references: [id], onDelete: Cascade)
   content          String
   occurredAt       DateTime // 發生時間
   emotionTag       EmotionTag
@@ -123,6 +124,8 @@ model EpisodicMemory {
   lastRetrievedAt  DateTime?
   source           MemorySource
   weight           Float        @default(1) // 權重（供遺忘／檢索排序使用）
+  relatedUserId    String? // 這段記憶與哪位使用者相關（E-5 關係加權檢索用）
+  relatedUser      User?        @relation(fields: [relatedUserId], references: [id], onDelete: SetNull)
   createdAt        DateTime     @default(now())
 
   @@map("episodic_memories")
@@ -131,7 +134,7 @@ model EpisodicMemory {
 model SemanticMemory {
   id          String    @id @default(cuid())
   characterId String
-  character   Character @relation(fields: [characterId], references: [id])
+  character   Character @relation(fields: [characterId], references: [id], onDelete: Cascade)
   fact        String // 去情境化事實
   about       String // 對象（關於誰／什麼）
   createdAt   DateTime  @default(now())
@@ -142,7 +145,7 @@ model SemanticMemory {
 model ProceduralRule {
   id              String    @id @default(cuid())
   characterId     String
-  character       Character @relation(fields: [characterId], references: [id])
+  character       Character @relation(fields: [characterId], references: [id], onDelete: Cascade)
   situation       String // 情境
   responsePattern String // 回應模式
   weight          Float     @default(1)
@@ -155,7 +158,7 @@ model ProceduralRule {
 model EmotionState {
   id          String    @id @default(cuid())
   characterId String    @unique
-  character   Character @relation(fields: [characterId], references: [id])
+  character   Character @relation(fields: [characterId], references: [id], onDelete: Cascade)
 
   calm   Float @default(100) // 平靜
   joy    Float @default(0) // 愉悅
@@ -172,9 +175,9 @@ model EmotionState {
 model Relationship {
   id          String @id @default(cuid())
   characterId String
-  character   Character @relation(fields: [characterId], references: [id])
+  character   Character @relation(fields: [characterId], references: [id], onDelete: Cascade)
   userId      String
-  user        User   @relation(fields: [userId], references: [id])
+  user        User      @relation(fields: [userId], references: [id], onDelete: Cascade)
 
   intimacy         Int               @default(0) // 親密度 0~100
   trust            Int               @default(0) // 信任度 0~100
@@ -195,7 +198,7 @@ model Relationship {
 model SentimentLedgerEntry {
   id             String       @id @default(cuid())
   relationshipId String
-  relationship   Relationship @relation(fields: [relationshipId], references: [id])
+  relationship   Relationship @relation(fields: [relationshipId], references: [id], onDelete: Cascade)
   date           DateTime
   event          String
   weight         Float // 允許正負：正向事件為正值，負向事件為負值