feat(pos): scaffold project structure and Flask app

pos/config.py

@@ -0,0 +1,21 @@
+import os
+
+MASTER_DB_URL = os.environ.get(
+    "MASTER_DB_URL",
+    "postgresql://nexus:nexus_autoparts_2026@localhost/nexus_autoparts"
+)
+
+TENANT_DB_URL_TEMPLATE = os.environ.get(
+    "TENANT_DB_URL_TEMPLATE",
+    "postgresql://nexus:nexus_autoparts_2026@localhost/{db_name}"
+)
+
+JWT_SECRET = os.environ.get("POS_JWT_SECRET", "nexus-pos-secret-change-in-prod-2026")
+JWT_ACCESS_EXPIRES = 28800    # 8 hours (full shift)
+JWT_REFRESH_EXPIRES = 2592000 # 30 days
+
+PIN_MAX_ATTEMPTS_PER_MINUTE = 5
+PIN_LOCKOUT_THRESHOLD = 10
+PIN_LOCKOUT_MINUTES = 15
+
+TENANT_TEMPLATE_DB = "tenant_template"