Fix receipt parsing quality and approval endpoint

Receipt quality: replace LLM amount/date extraction with regex.
LLM was hallucinating 2021/2022 dates and returning '198.40 USD' strings.
Amounts now use deterministic regex (Total:/Grand Total:/Amount Due:).
Dates: filename timestamp > OCR regex > today (no LLM date guessing).
LLM only asked for vendor name + product category.

Approval: fix GET /approval/pending 500 by using correct column
name 'started_at' instead of 'created_at' (which does not exist).

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

agent_service/routers/approval.py

@@ -33,8 +33,8 @@ async def list_pending():
         raise HTTPException(status_code=status.HTTP_503_SERVICE_UNAVAILABLE, detail='DB not ready')
     async with pool.acquire(timeout=10) as conn:
         rows = await conn.fetch(
-            'SELECT directive_id, agent_name, action_type, description, created_at, context_data '
-            'FROM ab_directive_log WHERE status = $1 ORDER BY created_at ASC',
+            'SELECT directive_id, agent_name, action_type, description, started_at, context_data '
+            'FROM ab_directive_log WHERE status = $1 ORDER BY started_at ASC',
             'pending_approval',
         )
     return [
@@ -43,7 +43,7 @@ async def list_pending():
             agent=r['agent_name'] or '',
             action=r['action_type'] or '',
             description=r['description'] or '',
-            created_at=str(r['created_at']),
+            created_at=str(r['started_at'] or ''),
             context=r['context_data'] or {},
         )
         for r in rows