feat: skills for artifacts (#13525)

Co-authored-by: Dibyo Majumdar <dibyo@openai.com>

codex-rs/skills/src/assets/samples/spreadsheets/references/workbook.md

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+# Workbook API
+
+Use `Workbook` to create, edit, recalculate, and export spreadsheet artifacts.
+
+## Lifecycle
+
+```js
+const workbook = Workbook.create();
+const sheet = workbook.worksheets.add("Sheet1");
+```
+
+- `Workbook.create()` starts a new workbook.
+- `await SpreadsheetFile.importXlsx(await FileBlob.load("book.xlsx"))` imports an existing workbook.
+- `workbook.recalculate()` evaluates formulas.
+- `await SpreadsheetFile.exportXlsx(workbook)` exports a saveable `.xlsx` blob.
+
+## Worksheets
+
+- `workbook.worksheets.add(name)` adds or returns a worksheet.
+- `workbook.worksheets.getItem(nameOrIndex)` fetches an existing sheet.
+- `workbook.worksheets.getActiveWorksheet()` returns the active sheet when relevant.
+
+## Charts And Images
+
+For charts that must survive `.xlsx` export reliably, prefer mutating the returned chart object directly:
+
+```js
+const chart = sheet.charts.add("line");
+chart.setPosition("A10", "H24");
+chart.title = "Cash runway";
+chart.categories = ["Month 0", "Month 1", "Month 2"];
+
+const series = chart.series.add("Savings");
+series.values = [6000, 6850, 7700];
+```
+
+This authoring path is more reliable than some one-shot chart construction styles, which can produce workbook objects that appear fine in memory but export to empty or misplaced charts.
+
+For worksheet images, prefer a `blob` payload:
+
+```js
+const fs = await import("node:fs/promises");
+const bytes = await fs.readFile("artifacts/chart-preview.png");
+const blob = bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.byteLength);
+
+sheet.images.add({
+  blob,
+  contentType: "image/png",
+  anchor: {
+    from: { row: 10, col: 0 },
+    to: { row: 24, col: 8 },
+  },
+});
+```
+
+## QA
+
+If the workbook includes charts or images, verify the final sheet layout after export, not just before export:
+
+```js
+const png = await workbook.render({ sheet: 0, format: "png" });
+```
+
+Use rendered previews to confirm both of these points:
+
+- The chart or image actually appears in the exported workbook.
+- It lands where a user will see it without scrolling far past the main table.
+
+Merged cells and tall autofit rows can push drawings far below the fold even when the drawing exists and is correctly attached to the sheet.
+
+## Output
+
+Prefer saving generated files into `artifacts/` so the user can inspect the workbook directly.