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>

agent_service/memory/operational_store.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+import json
 import logging
 from datetime import datetime, timedelta
 
@@ -11,12 +12,14 @@ class OperationalStore:
 
     async def store(self, scope, summary, raw_data=None, ttl_days=90, source_directive_id=None):
         expires_at = datetime.utcnow() + timedelta(days=ttl_days)
+        # asyncpg JSONB column expects a JSON string, not a Python dict
+        raw_data_json = json.dumps(raw_data) if raw_data is not None else None
         async with self._pool.acquire(timeout=10) as conn:
             await conn.execute(
                 """INSERT INTO ab_operational_memory
                    (scope, summary, raw_data, source_directive_id, expires_at)
                    VALUES ($1, $2, $3, $4, $5)""",
-                scope, summary, raw_data, source_directive_id, expires_at)
+                scope, summary, raw_data_json, source_directive_id, expires_at)
 
     async def get_recent(self, scope, limit=10):
         async with self._pool.acquire(timeout=10) as conn: