feat: add Sign PDF tool (draw/type/upload signatures, place on a PDF) (#370)

Draw, type, or upload a signature and place resizable/rotatable copies across PDF pages; output flattened server-side with PyMuPDF. Visual electronic signature, not cryptographic. New interactive-sign display mode (pdf.js + Konva) and a custom docs-pool route.

packages/doc-engine/src/index.ts

@@ -45,6 +45,7 @@ export {
   pdfMetadataSetPy,
   pdfPageCountPy,
   pdfRedactPy,
+  pdfSignPy,
   pdfTextPy,
   pdfToWordPy,
 } from "./python-docs.js";

packages/doc-engine/src/python-docs.ts

@@ -1,4 +1,5 @@
 import { runDocsScript } from "@snapotter/ai";
+import type { SignPlacement } from "@snapotter/shared";
 
 /** Page count via the docs-profile Python dispatcher (pikepdf). */
 export async function pdfPageCountPy(absPath: string): Promise<number> {
@@ -119,3 +120,30 @@ export async function htmlToPdfPy(
     throw new Error(`doc_html_pdf failed: ${parsed.error}`);
   }
 }
+
+/** Stamp signature images onto a PDF (PyMuPDF insert_image), flattened. */
+export async function pdfSignPy(
+  inPath: string,
+  outPath: string,
+  signatures: string[],
+  placements: SignPlacement[],
+): Promise<{ placed: number }> {
+  const stdout = await runDocsScript("doc_sign", {
+    input: inPath,
+    output: outPath,
+    signatures,
+    placements,
+  });
+  const parsed = JSON.parse(stdout.trim()) as {
+    ok?: boolean;
+    placed?: number;
+    error?: string;
+  };
+  if (parsed.error) {
+    throw new Error(`doc_sign failed: ${parsed.error}`);
+  }
+  if (typeof parsed.placed !== "number") {
+    throw new Error(`doc_sign failed: ${stdout.slice(0, 200)}`);
+  }
+  return { placed: parsed.placed };
+}