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/candidate_subs.py

@@ -0,0 +1,14 @@
+from typing import Dict, Set
+
+def candidate_subs(nav: Dict[str, Dict])-> Set[str]:
+    nav_sub_candidates: Set[str] = set()
+    for label, data in (nav.get("cats") or {}).items():
+        top_slug = (data or {}).get("slug")
+        if not top_slug:
+            continue
+        for s in (data.get("subs") or []):
+            sub_slug = (s.get("slug") or "").strip()
+            if sub_slug:
+                nav_sub_candidates.add(f"/{top_slug}/{sub_slug}")
+    return nav_sub_candidates
+