feat: implement chat and conversation history management with database schema and API endpoints

db/query/chat.sql

@@ -0,0 +1,46 @@
+-- name: CreateConversation :one
+INSERT INTO conversations (user_id, status)
+VALUES ($1, $2)
+RETURNING *;
+
+-- name: UpdateConversationStatus :one
+UPDATE conversations
+SET status = $2, mod_id = COALESCE($3, mod_id), closed_at = $4, updated_at = NOW()
+WHERE id = $1
+RETURNING *;
+
+-- name: CreateMessage :one
+INSERT INTO messages (conversation_id, sender_id, content)
+VALUES ($1, $2, $3)
+RETURNING *;
+
+-- name: GetMessagesByConversation :many
+SELECT * FROM messages
+WHERE conversation_id = $1
+  AND (sqlc.narg('cursor_id')::uuid IS NULL OR id < sqlc.narg('cursor_id')::uuid)
+ORDER BY created_at DESC
+LIMIT sqlc.arg('limit');
+
+-- name: GetConversationsByIDs :many
+SELECT * FROM conversations WHERE id = ANY($1::uuid[]);
+
+-- name: GetMessagesByIDs :many
+SELECT * FROM messages WHERE id = ANY($1::uuid[]);
+
+-- name: CreateChatbotHistory :one
+INSERT INTO chatbot_histories (user_id, question, answer)
+VALUES ($1, $2, $3)
+RETURNING *;
+
+-- name: GetChatbotHistory :many
+SELECT * FROM (
+    SELECT * FROM chatbot_histories
+    WHERE user_id = $1
+      AND (sqlc.narg('cursor_id')::uuid IS NULL OR id < sqlc.narg('cursor_id')::uuid)
+    ORDER BY created_at DESC
+    LIMIT sqlc.arg('limit')
+) sub
+ORDER BY created_at ASC;
+
+-- name: GetChatbotHistoriesByIDs :many
+SELECT * FROM chatbot_histories WHERE id = ANY($1::uuid[]);