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/build_snapshot/tools/valid_subs.py

@@ -0,0 +1,16 @@
+from typing import Dict, Set
+
+# make valid subs for ewch top in nav
+def valid_subs(nav: Dict[str, Dict])->Dict[str, Set[str]] :
+    valid_subs_by_top: Dict[str, Set[str]] = {}
+    for label, data in (nav.get("cats") or {}).items():
+        top_slug = (data or {}).get("slug")
+        if not top_slug:
+            continue
+        subs_set = {
+            (s.get("slug") or "").strip()
+            for s in (data.get("subs") or [])
+            if s.get("slug")
+        }
+        valid_subs_by_top[top_slug] = subs_set
+    return valid_subs_by_top