test(13-01): add failing aiCoordsToPagePdfSpace unit tests

- Add ai-coords.test.ts with 3 test cases covering US Letter (612x792 pts)
- Tests import from lib/ai/field-placement which does not exist yet (RED phase)
- Cases: text field near top, checkbox near bottom-right, client-sig at center

teressa-copeland-homes/src/lib/pdf/__tests__/ai-coords.test.ts

@@ -0,0 +1,91 @@
+/**
+ * Unit tests for aiCoordsToPagePdfSpace — AI top-left percentage coordinates to PDF bottom-left points.
+ *
+ * AI models return positions with top-left origin (0,0 = top-left corner of page).
+ * PDF user space uses bottom-left origin (0,0 = bottom-left corner of page).
+ * The conversion must flip the Y axis and multiply percentages by page dimensions.
+ *
+ * US Letter: 612 × 792 pts at 72 DPI.
+ */
+
+import { aiCoordsToPagePdfSpace } from '../../../lib/ai/field-placement';
+
+const US_LETTER_W = 612;  // pts
+const US_LETTER_H = 792;  // pts
+
+describe('aiCoordsToPagePdfSpace — AI top-left percentage to PDF bottom-left points', () => {
+  test('text field near top of page', () => {
+    // xPct=10, yPct=5, widthPct=30, heightPct=5
+    // x = 612 * 0.10 = 61.2
+    // fieldH = 792 * 0.05 = 39.6
+    // screenY = 792 * 0.05 = 39.6
+    // y = 792 - 39.6 - 39.6 = 712.8
+    const result = aiCoordsToPagePdfSpace(
+      {
+        page: 1,
+        fieldType: 'text',
+        xPct: 10,
+        yPct: 5,
+        widthPct: 30,
+        heightPct: 5,
+        prefillValue: '',
+      },
+      US_LETTER_W,
+      US_LETTER_H,
+    );
+    expect(result.x).toBeCloseTo(61.2, 1);
+    expect(result.y).toBeCloseTo(712.8, 1);
+    expect(result.width).toBeCloseTo(183.6, 1);
+    expect(result.height).toBeCloseTo(39.6, 1);
+  });
+
+  test('checkbox near bottom-right', () => {
+    // xPct=90, yPct=95, widthPct=3, heightPct=3
+    // x = 612 * 0.90 = 550.8
+    // fieldH = 792 * 0.03 = 23.76
+    // screenY = 792 * 0.95 = 752.4
+    // y = 792 - 752.4 - 23.76 = 15.84
+    const result = aiCoordsToPagePdfSpace(
+      {
+        page: 1,
+        fieldType: 'checkbox',
+        xPct: 90,
+        yPct: 95,
+        widthPct: 3,
+        heightPct: 3,
+        prefillValue: '',
+      },
+      US_LETTER_W,
+      US_LETTER_H,
+    );
+    expect(result.x).toBeCloseTo(550.8, 1);
+    expect(result.y).toBeCloseTo(15.84, 1);
+    expect(result.width).toBeCloseTo(18.36, 1);
+    expect(result.height).toBeCloseTo(23.76, 1);
+  });
+
+  test('client-signature field at exact center', () => {
+    // xPct=50, yPct=50, widthPct=20, heightPct=5
+    // x = 612 * 0.50 = 306
+    // fieldH = 792 * 0.05 = 39.6
+    // screenY = 792 * 0.50 = 396
+    // y = 792 - 396 - 39.6 = 356.4
+    const result = aiCoordsToPagePdfSpace(
+      {
+        page: 1,
+        fieldType: 'client-signature',
+        xPct: 50,
+        yPct: 50,
+        widthPct: 20,
+        heightPct: 5,
+        prefillValue: '',
+      },
+      US_LETTER_W,
+      US_LETTER_H,
+    );
+    expect(result.x).toBeCloseTo(306, 1);
+    expect(result.y).toBeCloseTo(356.4, 1);
+    expect(result.width).toBeCloseTo(122.4, 1);
+    expect(result.height).toBeCloseTo(39.6, 1);
+  });
+});