Add review stage coverage and fix XML tax deduplication

- Reviewer now sends all pages to the review VLM alongside extracted JSON.

- XML builder deduplicates account.tax records by rate.

- XML builder raises on confidence below min_confidence_threshold.

- Adds fractional tax-rate support with stable external IDs.

- Adds expected_invoice.xml fixture, reviewer tests, and XML regression tests.

tests/test_reviewer.py

@@ -0,0 +1,85 @@
+"""Tests for the vision review stage."""
+
+from __future__ import annotations
+
+import pytest
+from PIL import Image
+
+from odoo_ocr.config import Settings
+from odoo_ocr.pipeline.reviewer import review_invoice
+from odoo_ocr.schemas import ExtractedInvoice, ReviewResult
+from tests.conftest import FakeVLMClient
+
+
+def make_invoice() -> ExtractedInvoice:
+    return ExtractedInvoice(
+        vendor_name="Acme",
+        invoice_number="INV-1",
+        invoice_date="2024-01-01",
+    )
+
+
+@pytest.mark.asyncio
+async def test_review_returns_parsed_result() -> None:
+    client = FakeVLMClient(
+        responses={
+            "invoice review assistant": {
+                "valid": True,
+                "confidence": 0.95,
+                "issues": [],
+                "corrected_invoice": None,
+            }
+        }
+    )
+    result = await review_invoice(
+        make_invoice(), [Image.new("RGB", (10, 10))], client, Settings()
+    )
+    assert isinstance(result, ReviewResult)
+    assert result.valid is True
+    assert result.confidence == 0.95
+
+
+@pytest.mark.asyncio
+async def test_review_sends_all_pages() -> None:
+    client = FakeVLMClient(
+        responses={
+            "invoice review assistant": {
+                "valid": True,
+                "confidence": 0.90,
+                "issues": [],
+                "corrected_invoice": None,
+            }
+        }
+    )
+    pages = [Image.new("RGB", (10, 10)) for _ in range(3)]
+    await review_invoice(make_invoice(), pages, client, Settings())
+    assert client.calls[-1]["image_count"] == len(pages)
+
+
+@pytest.mark.asyncio
+async def test_review_preserves_corrected_invoice() -> None:
+    corrected = {
+        "vendor_name": "Acme",
+        "invoice_number": "INV-1",
+        "invoice_date": "2024-01-01",
+        "line_items": [],
+        "subtotal": 100.0,
+        "tax_total": 0.0,
+        "total": 100.0,
+    }
+    client = FakeVLMClient(
+        responses={
+            "invoice review assistant": {
+                "valid": True,
+                "confidence": 0.95,
+                "issues": [{"field": "total", "severity": "warning", "message": "rounded"}],
+                "corrected_invoice": corrected,
+            }
+        }
+    )
+    result = await review_invoice(
+        make_invoice(), [Image.new("RGB", (10, 10))], client, Settings()
+    )
+    assert result.corrected_invoice is not None
+    assert result.corrected_invoice.total == 100.0
+    assert result.issues[0].severity == "warning"