feat(coach): add encrypted conversation-summary columns (migration 0114)

prisma/migrations/0114_v1110_coach_conversation_summary/migration.sql

@@ -0,0 +1,5 @@
+-- v1.11.0 — rolling encrypted conversation summary for the Coach.
+-- Additive only; safe on a populated table (nullable + defaulted).
+ALTER TABLE "coach_conversations" ADD COLUMN IF NOT EXISTS "summary_encrypted" BYTEA;
+ALTER TABLE "coach_conversations" ADD COLUMN IF NOT EXISTS "summary_updated_at" TIMESTAMP(3);
+ALTER TABLE "coach_conversations" ADD COLUMN IF NOT EXISTS "summary_turn_count" INTEGER NOT NULL DEFAULT 0;

prisma/schema.prisma

@@ -2629,6 +2629,13 @@ model CoachConversation {
   createdAt DateTime @default(now()) @map("created_at")
   updatedAt DateTime @updatedAt @map("updated_at")
 
+  // v1.11.0 — rolling encrypted summary of the elided older turns, so a long
+  // conversation keeps memory of what came before without re-sending every
+  // turn to the provider. AES-256-GCM (same codec as CoachMessage.encrypted).
+  summaryEncrypted Bytes?    @map("summary_encrypted")
+  summaryUpdatedAt DateTime? @map("summary_updated_at")
+  summaryTurnCount Int       @default(0) @map("summary_turn_count")
+
   user     User           @relation(fields: [userId], references: [id], onDelete: Cascade)
   messages CoachMessage[]