v0.1.32 - Mix Calculator search, ingredient categories, throughput tidy-up

- Mix Calculator: searchable Mix Name picker (mirrors Throughput search)
- Ingredients Editor: add manual Category column; used to order Mix Calculator output
- Mix Calculator: surface formula-only mixes (no product yet) via -mix_id sentinel
- Throughput: remove unused For order / For stock destination controls from composer
- Editor change history: show timestamps in local time (stored UTC) instead of raw UTC

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/tests/test_costing_engine.py

@@ -482,7 +482,13 @@ def test_mix_calculator_endpoints_respect_owner_visibility():
         options_response = client.get("/api/mix-calculator/options", cookies=superadmin_cookies)
         assert options_response.status_code == 200
         options_payload = options_response.json()
-        assert len(options_payload["products"]) == 84
+        # 83 product-backed mixes + 1 formula-only mix ("Hi Carb Popcorn", which
+        # has a mix-master formula but no product yet, surfaced via a negative
+        # product_id sentinel so a new mix is usable before a product is linked).
+        assert len(options_payload["products"]) == 84 + 1
+        formula_only = [product for product in options_payload["products"] if product["product_id"] < 0]
+        assert len(formula_only) == 1
+        assert formula_only[0]["unit_size_kg"] == 0
         seeded_product = next(
             product
             for product in options_payload["products"]