feat: add pagination to conversation list and history - #348

Overview

This PR adds pagination to the conversation list and conversation history endpoints so that large account histories load quickly, and wires the chat sidebar to consume paginated responses via infinite scroll with a "load more" fallback. It also adds tests covering pagination bounds and defaults.

Related Issue

Changes

📄 Backend Pagination

• [MODIFY] app/chat/api.py

  • GET /chat/conversations now accepts page and per_page query params and returns {items, page, pages, total}.
  • Conversation history endpoint paginates messages for long conversations.
  • Defaults and bounds applied to page and per_page so out-of-range values are handled safely.

• [MODIFY] app/chat/routes.py

  • Route handlers pass through the new page / per_page params and return the paginated payload shape.

🖥️ Frontend

• [MODIFY] app/static/js/chat.js
  • Chat sidebar fetches the next page when the user scrolls to the bottom (infinite scroll).
  • "Load more" button shown as a fallback when infinite scroll is not triggered.
  • Conversation history view requests additional message pages for long conversations.

✅ Tests

• [MODIFY] tests/test_chat.py

  • Coverage for pagination bounds and defaults on the conversation list and history endpoints.

• [MODIFY] tests/test_chat_api.py

  • API-level tests for page / per_page handling and the {items, page, pages, total} response shape.

Verification Results

pytest tests/test_chat.py tests/test_chat_api.py
✅ pagination bounds and defaults covered
✅ conversation list returns {items, page, pages, total}
✅ conversation history paginates messages

Closes #36