feat(odin): ai_conversations table + conversation_id on messages

prisma/migrations/20260608140000_add_ai_conversations/migration.sql

@@ -0,0 +1,32 @@
+-- Multi-conversation Odin: conversations table + conversation_id on messages.
+
+CREATE TABLE `ai_conversations` (
+  `id` INTEGER NOT NULL AUTO_INCREMENT,
+  `user_id` INTEGER NOT NULL,
+  `title` VARCHAR(255) NOT NULL,
+  `created_at` TIMESTAMP(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0),
+  `updated_at` TIMESTAMP(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0),
+  PRIMARY KEY (`id`),
+  INDEX `idx_ai_conv_user` (`user_id`, `id`)
+) DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+
+ALTER TABLE `ai_chat_messages`
+  ADD COLUMN `conversation_id` INTEGER NULL AFTER `user_id`;
+
+-- Backfill: one conversation per user who has messages ("keep as first conversation").
+INSERT INTO `ai_conversations` (`user_id`, `title`, `created_at`, `updated_at`)
+SELECT `user_id`, 'Konverzace', NOW(), NOW()
+FROM `ai_chat_messages`
+GROUP BY `user_id`;
+
+UPDATE `ai_chat_messages` m
+JOIN `ai_conversations` c ON c.`user_id` = m.`user_id`
+SET m.`conversation_id` = c.`id`;
+
+-- Enforce: drop old per-user index, NOT NULL, FK (cascade), per-conversation index.
+ALTER TABLE `ai_chat_messages`
+  DROP INDEX `idx_ai_chat_user`,
+  MODIFY `conversation_id` INTEGER NOT NULL,
+  ADD CONSTRAINT `fk_ai_chat_conv` FOREIGN KEY (`conversation_id`)
+    REFERENCES `ai_conversations`(`id`) ON DELETE CASCADE,
+  ADD INDEX `idx_ai_chat_conv` (`conversation_id`, `id`);

prisma/schema.prisma

@@ -89,14 +89,27 @@ model ai_usage {
   @@index([created_at], map: "idx_ai_usage_created")
 }
 
+model ai_conversations {
+  id         Int                @id @default(autoincrement())
+  user_id    Int
+  title      String             @db.VarChar(255)
+  created_at DateTime           @default(now()) @db.Timestamp(0)
+  updated_at DateTime           @default(now()) @updatedAt @db.Timestamp(0)
+  messages   ai_chat_messages[]
+
+  @@index([user_id, id], map: "idx_ai_conv_user")
+}
+
 model ai_chat_messages {
   id              Int              @id @default(autoincrement())
   user_id         Int
+  conversation_id Int
   role            String           @db.VarChar(20)
   content         String           @db.Text
   created_at      DateTime         @default(now()) @db.Timestamp(0)
+  conversation    ai_conversations @relation(fields: [conversation_id], references: [id], onDelete: Cascade)
 
-  @@index([user_id, id], map: "idx_ai_chat_user")
+  @@index([conversation_id, id], map: "idx_ai_chat_conv")
 }
 
 model bank_accounts {