feat(pos): add inventory-aware chat context (#31) and VIN decoder (#17)

Chat now fetches tenant inventory summary (brands, counts, low-stock)
and injects it into the AI system prompt so responses prioritize local
stock. VIN decoder uses free NHTSA vPIC API to decode 17-char VINs and
auto-fills the vehicle selector dropdowns when a catalog match is found.

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

pos/blueprints/chat_bp.py

@@ -23,8 +23,23 @@ def chat():
 
     history = body.get("history") or []
 
-    # Call AI
-    ai_response = ai_chat.chat(user_message, history)
+    # Fetch inventory context so the AI knows what this tenant has in stock
+    inventory_context = None
+    tenant_for_context = None
+    try:
+        tenant_for_context = get_tenant_conn(g.tenant_id)
+        inventory_context = ai_chat.get_inventory_context(tenant_for_context, g.branch_id)
+    except Exception:
+        pass
+    finally:
+        if tenant_for_context:
+            try:
+                tenant_for_context.close()
+            except Exception:
+                pass
+
+    # Call AI with inventory context
+    ai_response = ai_chat.chat(user_message, history, inventory_context=inventory_context)
 
     search_results = []
     vehicle_match = None