Add OcrResponse schema and tighten invoice validation

- Adds OcrResponse Pydantic schema for OCR branch JSON output.

- Validates invoice_date and due_date as strict ISO 8601 calendar dates.

- Adds field descriptions to InvoiceLineItem for clearer VLM prompts.

- Expands schema tests for dates, decimal coercion, negatives, and line_items_sum().

tests/test_schemas.py

@@ -0,0 +1,84 @@
+"""Tests for invoice schema validation."""
+
+from __future__ import annotations
+
+from decimal import Decimal
+
+import pytest
+from pydantic import ValidationError
+
+from odoo_ocr.schemas import ExtractedInvoice, InvoiceLineItem
+
+
+def test_accepts_valid_iso_dates() -> None:
+    invoice = ExtractedInvoice(
+        vendor_name="A",
+        invoice_number="1",
+        invoice_date="2024-01-01",
+        due_date="2024-02-01",
+    )
+    assert invoice.invoice_date == "2024-01-01"
+    assert invoice.due_date == "2024-02-01"
+
+
+def test_rejects_non_iso_date_format() -> None:
+    with pytest.raises(ValidationError, match="ISO 8601"):
+        ExtractedInvoice(
+            vendor_name="A",
+            invoice_number="1",
+            invoice_date="May 1, 2024",
+        )
+
+
+def test_rejects_invalid_calendar_date() -> None:
+    with pytest.raises(ValidationError, match="not a valid calendar date"):
+        ExtractedInvoice(
+            vendor_name="A",
+            invoice_number="1",
+            invoice_date="2024-02-30",
+        )
+
+
+def test_due_date_optional() -> None:
+    invoice = ExtractedInvoice(
+        vendor_name="A",
+        invoice_number="1",
+        invoice_date="2024-01-01",
+    )
+    assert invoice.due_date is None
+
+
+def test_invoice_line_item_decimal_coercion() -> None:
+    line = InvoiceLineItem(
+        description="Widgets",
+        quantity="2",
+        unit_price="10.5",
+        total_price="21.0",
+        tax_rate="20",
+    )
+    assert line.quantity == Decimal("2")
+    assert line.unit_price == Decimal("10.5")
+    assert line.total_price == Decimal("21.0")
+    assert line.tax_rate == Decimal("20")
+
+
+def test_invoice_line_item_rejects_negative_values() -> None:
+    with pytest.raises(ValidationError):
+        InvoiceLineItem(description="X", quantity=-1)
+    with pytest.raises(ValidationError):
+        InvoiceLineItem(description="X", unit_price=-1)
+    with pytest.raises(ValidationError):
+        InvoiceLineItem(description="X", tax_rate=-5)
+
+
+def test_line_items_sum() -> None:
+    invoice = ExtractedInvoice(
+        vendor_name="A",
+        invoice_number="1",
+        invoice_date="2024-01-01",
+        line_items=[
+            InvoiceLineItem(description="X", total_price=Decimal("100")),
+            InvoiceLineItem(description="Y", total_price=Decimal("50.50")),
+        ],
+    )
+    assert invoice.line_items_sum() == Decimal("150.50")