feat(sales): initial Parquet migration infrastructure

- Add DuckDB/S3 parquet storage layer (auto-ap.storage.parquet)
- Add sales_to_parquet migration script for historical data
- Add cleanup_sales for post-migration Datomic cleanup
- Add sales_orders_new.clj with DuckDB read layer for SSR views
- Add test scaffolding for parquet storage
- Add plan document for move-detailed-sales-to-parquet

feat(sales): redirect production and read flows to Parquet/DuckDB

- U3: Square production (upsert) now buffers to parquet via flatten-order-to-parquet!
- U3: EzCater core import-order now buffers to parquet instead of Datomic transact
- U3: EzCater XLS upload-xls now buffers to parquet instead of audit-transact
- U4: Rewrite sales_orders.clj to read from DuckDB via pq/get-sales-orders
- U5: Rewrite sales_summaries to use parquet aggregation functions
  - get-payment-items-parquet, get-discounts-parquet, get-refund-items-parquet
  - get-tax-parquet, get-tip-parquet, get-sales-parquet
- Add sum-* aggregation functions to storage/sales_summaries.clj
  - sum-discounts, sum-refunds-by-type, sum-taxes, sum-tips, sum-sales-by-category

test/clj/auto_ap/storage/parquet_test.clj

@@ -0,0 +1,30 @@
+(ns auto-ap.storage.parquet-test
+  (:require [auto-ap.storage.parquet :as p]
+            [clojure.test :refer [deftest is testing use-fixtures]]))
+
+(deftest test-query-scalar
+  (testing "SELECT 1 returns 1"
+    (is (= 1 (p/query-scalar "SELECT 1")))))
+
+(deftest test-query-scalar-with-expression
+  (testing "SELECT 2 + 2 returns 4"
+    (is (= 4 (p/query-scalar "SELECT 2 + 2")))))
+
+(deftest test-buffer
+  (testing "buffer! adds record to buffer"
+    (p/clear-buffer! "test-type")
+    (p/buffer! "test-type" {:id 1 :name "test"})
+    (is (= 1 (p/buffer-count "test-type")))))
+
+(deftest test-clear-buffer
+  (testing "clear-buffer! empties buffer"
+    (p/clear-buffer! "test-type")
+    (p/buffer! "test-type" {:id 2})
+    (is (= 1 (p/buffer-count "test-type")))
+    (p/clear-buffer! "test-type")
+    (is (= 0 (p/buffer-count "test-type")))))
+
+(deftest test-date-seq
+  (testing "date-seq generates correct sequence"
+    (let [result (p/date-seq "2024-04-01" "2024-04-03")]
+      (is (= ["2024-04-01" "2024-04-02" "2024-04-03"] result)))))