Add GET /api/search/async that returns HTTP 202 immediately and streams
scrape results via SSE to avoid nginx 120s timeouts on slow eBay searches.
Backend:
- New GET /api/search/async endpoint submits scraping to ThreadPoolExecutor
and returns {session_id, status: "queued"} before scrape begins
- Background worker runs same pipeline as synchronous search, pushing
typed SSE events: "listings" (initial batch), "update" (enrichment),
"market_price", and None sentinel
- Existing GET /api/updates/{session_id} passes new event types through
as-is (already a generic pass-through); deadline extended to 150s
- Module-level _search_executor (max_workers=4) caps concurrent scrape sessions
Frontend (search.ts):
- search() now calls /api/search/async instead of /api/search
- loading stays true until first "listings" SSE event arrives
- _openUpdates() handles new typed events: "listings", "market_price",
"update"; legacy untyped enrichment events still handled
- cancelSearch() now also closes any open SSE stream
Tests: tests/test_async_search.py (6 tests) covering 202 response,
session_id registration in _update_queues, empty query path, UUID format,
and no-Chromium guarantee. All 159 pre-existing tests still pass.
Closes#49. Also closes Forgejo issue #1 (SSE enrichment streaming, already
implemented; async search completes the picture).
