Upload Invoice PDF for AI Extraction

    Upload an invoice PDF file for automated AI-powered extraction and processing.

    **Processing Flow:**
    1. PDF is uploaded to S3 storage
    2. Background LangGraph workflow is queued for intelligent processing
    3. API returns immediately (202 Accepted)
    4. Background workflow processing:
       - Extracts invoice data using Reducto AI
       - Classifies document type (invoice/credit note)
       - Validates document is from your business
       - Matches or creates customer using AI semantic matching
       - Detects semantic duplicates
       - Validates extracted data
       - Creates invoice record
    5. Extracted invoice appears in GET /invoices/ list

    **File Requirements:**
    - Format: PDF or images (PNG, JPEG, GIF, BMP, TIFF, HEIC)
    - Size: Maximum 50MB for PDF, 10-20MB for images
    - Content: Invoice document or scanned invoice image
    - Content-Type validation: File content is verified to match declared type

    **Extraction Quality:**
    - Fields with ≥90% confidence are auto-filled
    - Fields below threshold require manual review
    - Line items with parsing errors are flagged
    - Total mismatches (>1% or >$10) trigger review flag

    **Duplicate Detection:**
    - AI compares with last 100 invoices
    - High confidence duplicates (≥90%) are blocked
    - Medium confidence (70-89%) are flagged for review
    - Low confidence (<70%) are processed normally

    **Access Control:**
    - Requires partner authentication
    - Business must belong to authenticated partner