Use remote Chromium container instead of local Puppeteer launch

- Add browserless/chromium container to docker-compose
- Add docker-compose.dev.yml for local dev (Chromium on port 3001)
- Browser scraper connects via WebSocket (CHROMIUM_WS env var)
- Falls back to local launch if CHROMIUM_WS not set
- Remove Chromium install from Dockerfile (smaller image)
- Auto-reconnect on browser disconnect

Tested: remote Chromium connects in ~500ms, HG Spot scrapes in
~2.2s total. No longer blocks the Node.js event loop.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.example

@@ -1,3 +1,4 @@
 PORT=3000
 DATABASE_PATH=./data/pricehunter.db
 STORES_DIR=./stores
+CHROMIUM_WS=ws://localhost:3001