feat: initialize market app with browsing, product, and scraping code

Split from coop monolith. Includes:
- Market/browse/product blueprints
- Product sync API
- Suma scraping pipeline
- Templates for market, browse, and product views
- Dockerfile and CI workflow for independent deployment

scrape/persist_snapshot/_get.py

@@ -0,0 +1,3 @@
+def _get(d, key, default=None):
+    v = d.get(key)
+    return default if v in (None, "", [], {}) else v