Export: XMP-Metadatenblock und CreationDate/ModDate via pikepdf nachziehen

WeasyPrint 68.1 schreibt weder XMP noch Create-/ModDate ins PDF. Das Post-
Processing via pikepdf ergaenzt beide:

- Info-Dict: /CreationDate + /ModDate im PDF-Standardformat
  (D:YYYYMMDDHHmmSS+HHmm) aus Incident.created_at / updated_at
- XMP-Block mit Dublin Core (dc:title, dc:creator, dc:description,
  dc:subject, dc:language), PDF (pdf:Keywords) und XMP (CreatorTool,
  CreateDate, ModifyDate, MetadataDate) Namespaces

Damit werden die Exporte sowohl von klassischen Tools (Explorer, Finder)
als auch von DMS-Systemen (SharePoint, Bridge, Acrobat) vollstaendig
indexiert. Fallback: Bei Fehler im Post-Processing wird das Original-PDF
zurueckgegeben, Export schlaegt nie fehl.

src/report_generator.py

@@ -8,6 +8,7 @@ from collections import defaultdict
 from datetime import datetime
 from pathlib import Path
 
+import pikepdf
 from jinja2 import Environment, FileSystemLoader
 from weasyprint import HTML
 from docx import Document
@@ -536,6 +537,63 @@ def _build_export_metadata(
     }
 
 
+def _format_pdf_date(dt: datetime) -> str:
+    """PDF-Datumsformat: D:YYYYMMDDHHmmSS+HH'mm' (mit Zeitzone) oder Z (UTC)."""
+    if dt.tzinfo is None:
+        # Naive dt — als lokale TIMEZONE interpretieren
+        dt = dt.replace(tzinfo=TIMEZONE)
+    base = dt.strftime("D:%Y%m%d%H%M%S")
+    offset = dt.utcoffset()
+    if offset is None:
+        return base + "Z"
+    total_minutes = int(offset.total_seconds() // 60)
+    sign = "+" if total_minutes >= 0 else "-"
+    total_minutes = abs(total_minutes)
+    return f"{base}{sign}{total_minutes // 60:02d}'{total_minutes % 60:02d}'"
+
+
+def _enrich_pdf_metadata(pdf_bytes: bytes, meta: dict) -> bytes:
+    """PDF-Ausgabe um XMP-Metadaten und CreationDate/ModDate erweitern (post-process via pikepdf)."""
+    try:
+        buf_in = io.BytesIO(pdf_bytes)
+        with pikepdf.Pdf.open(buf_in) as pdf:
+            created: datetime = meta.get("created")
+            modified: datetime = meta.get("modified")
+            if created and created.tzinfo is None:
+                created = created.replace(tzinfo=TIMEZONE)
+            if modified and modified.tzinfo is None:
+                modified = modified.replace(tzinfo=TIMEZONE)
+
+            # Klassisches Info-Dict: CreationDate + ModDate nachziehen
+            if created:
+                pdf.docinfo["/CreationDate"] = pikepdf.String(_format_pdf_date(created))
+            if modified:
+                pdf.docinfo["/ModDate"] = pikepdf.String(_format_pdf_date(modified))
+
+            # XMP-Metadatenblock schreiben (Dublin Core + XMP + PDF Namespaces)
+            with pdf.open_metadata(set_pikepdf_as_editor=False) as xmp:
+                xmp["dc:title"] = meta.get("title", "")
+                xmp["dc:creator"] = [meta.get("author", "")]
+                xmp["dc:description"] = meta.get("subject", "")
+                if meta.get("keywords"):
+                    xmp["dc:subject"] = list(meta["keywords"])
+                xmp["dc:language"] = [meta.get("language", "de-DE")]
+                xmp["pdf:Keywords"] = meta.get("keywords_comma", "")
+                xmp["xmp:CreatorTool"] = meta.get("creator_app", "AegisSight Monitor")
+                if created:
+                    xmp["xmp:CreateDate"] = created.strftime("%Y-%m-%dT%H:%M:%S%z")
+                if modified:
+                    xmp["xmp:ModifyDate"] = modified.strftime("%Y-%m-%dT%H:%M:%S%z")
+                    xmp["xmp:MetadataDate"] = modified.strftime("%Y-%m-%dT%H:%M:%S%z")
+
+            buf_out = io.BytesIO()
+            pdf.save(buf_out)
+            return buf_out.getvalue()
+    except Exception as e:
+        logger.warning(f"PDF-Metadaten-Anreicherung (XMP/Dates) fehlgeschlagen: {e}")
+        return pdf_bytes
+
+
 async def generate_pdf(
     incident: dict, articles: list, fact_checks: list, snapshots: list,
     scope: str, creator: str, executive_summary_html: str,
@@ -614,6 +672,7 @@ async def generate_pdf(
             art["pub_date"] = pub[:10] if pub else ""
 
     pdf_bytes = HTML(string=html_content).write_pdf()
+    pdf_bytes = _enrich_pdf_metadata(pdf_bytes, meta)
     return pdf_bytes