fix: stamp SnapOtter as Producer on generated PDFs (#416)

Conversion engines wrote their own names into PDF metadata: LibreOffice,
Ghostscript, pdfcpu, WeasyPrint, and PDFKit all stamped Producer/Creator
on generated files. A new doc_scrub_meta docs-profile script (PyMuPDF)
rewrites both fields to SnapOtter and drops the stale XMP copy; the
worker applies it to the 25 PDF-generating tools before outputs reach
object storage. Best effort by design: any failure keeps the original
bytes and only logs a warning.

Deliberately untouched: tools that edit the user's own PDF and preserve
its metadata (qpdf edits, sign, flatten), encrypted outputs (copied
through), and pdfa-convert, where a metadata rewrite risks PDF/A
conformance.

Claude-Session: https://claude.ai/code/session_01XGB4pGvTvb7sUX4JN745U7

packages/ai/python/dispatcher.py

@@ -98,6 +98,7 @@ DOCS_SCRIPTS = {
     "doc_metadata",
     "doc_html_pdf",
     "doc_sign",
+    "doc_scrub_meta",
 }
 
 if DISPATCHER_PROFILE == "docs":

packages/ai/python/doc_scrub_meta.py

@@ -0,0 +1,49 @@
+"""Set the PDF Producer/Creator to SnapOtter on generated documents.
+Conversion engines stamp themselves (LibreOffice, Ghostscript, pdfcpu,
+WeasyPrint, PDFKit); from the user's point of view SnapOtter produced the
+file. Only runs for tools that GENERATE PDFs; pass-through edits keep the
+user's original metadata untouched.
+Args: {"path": in, "out": out}. Prints {"ok": true}."""
+import json
+import sys
+
+
+def main():
+    args = json.loads(sys.argv[1]) if len(sys.argv) > 1 else {}
+    path, out = args.get("path"), args.get("out")
+    if not path or not out:
+        print(json.dumps({"error": "missing path/out"}))
+        sys.exit(1)
+    try:
+        import fitz
+    except ImportError:
+        print(json.dumps({"error": "PyMuPDF not installed"}))
+        sys.exit(1)
+    try:
+        doc = fitz.open(path)
+        if doc.needs_pass:
+            # Encrypted output: pass it through untouched rather than
+            # re-encrypting. `out` must always exist for the caller.
+            doc.close()
+            import shutil
+
+            shutil.copyfile(path, out)
+            print(json.dumps({"ok": True, "skipped": "encrypted"}))
+            return
+        meta = doc.metadata or {}
+        meta["producer"] = "SnapOtter"
+        meta["creator"] = "SnapOtter"
+        doc.set_metadata(meta)
+        # XMP often carries the engine's own pdf:Producer; DocInfo is the
+        # canonical source for these files, so drop the stale copy.
+        doc.del_xml_metadata()
+        doc.save(out)
+        doc.close()
+        print(json.dumps({"ok": True}))
+    except Exception as exc:  # noqa: BLE001
+        print(json.dumps({"error": str(exc)}))
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()