feat: persist chat history

[kowyo-bot]

Persist per-user chat history in Postgres.

What’s included:

• New tables: chats, chat_messages (see scripts/db/migrate-chats.js)
• New APIs: GET/POST /api/chats, GET/DELETE /api/chats/[chatId], POST /api/chats/[chatId]/messages
• Chat UI now loads chat list + messages from DB, and sends chatId with requests
• /api/chat now persists user + assistant messages for the current chat
• Migration workflow runs both Better Auth + chat schema migrations (pnpm db:migrate:all)

To set up DB:

• Run

16chats@0.1.0 db:migrate:all /home/kowyo/.openclaw/workspace/16Chats
pnpm run db:migrate && pnpm run db:migrate:chats

16chats@0.1.0 db:migrate /home/kowyo/.openclaw/workspace/16Chats
npx @better-auth/cli migrate

 ELIFECYCLE  Command failed with exit code 1.
 ELIFECYCLE  Command failed with exit code 1. (or GitHub Actions → DB Migrate)