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/app/schemas/mix_calculator.py

@@ -27,6 +27,8 @@ class MixCalculatorSessionLineRead(BaseModel):
     mix_percentage: float
     unit: str
     rounding_decimals: int = 2
+    # Manual ingredient grouping used to order the calculator output.
+    category: str | None = None
     sort_order: int