feat: OCR via tesseract, dedup, category selection for expense receipts

- Dockerfile: install tesseract-ocr so Pillow+pytesseract can OCR receipt images
- operational_store: JSON-serialize raw_data before passing to asyncpg JSONB
- receipt_parser: add SHA256 hash + date extracted from filename timestamps
- expenses_agent: deduplicate receipts by hash before creating expense records
- expenses_agent: fetch all expensable Odoo products, pass list to LLM for
  category selection (Meals, Flights, etc.) per receipt
- expenses_agent: pass date_hint from filename (e.g. 20260509_180857.jpg -> 2026-05-09)
  as fallback when OCR text is unavailable
- expenses_tools: add get_expense_products() to fetch all expensable products

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -7,6 +7,7 @@ WORKDIR /app
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     gcc libpq-dev \
+    tesseract-ocr \
     && rm -rf /var/lib/apt/lists/*
 
 COPY requirements.txt .