feat: PDF-Export zusätzlich zu DOCX

Mac-Worker:
- pdf_export.py mit reportlab (pure Python, kein externes Tool)
- Nutzt dieselbe profile.docx-Konfig wie der DOCX-Renderer →
  strukturell identisch, nur andere Optik
- POST /api/export/pdf
- requirements: reportlab==4.2.5

LXC:
- Job.pdf_path neu (Migration: ALTER TABLE job ADD COLUMN)
- Pipeline-Step nach DOCX: PDF wird ebenfalls erzeugt
  (Progress: 90 DOCX → 95 PDF → 100 done)
- /api/jobs/{id}/download/pdf
- /api/jobs/{id}/retry löscht PDF mit, damit es neu erzeugt wird
- Frontend: zusätzlicher Download-Button "PDF" (vorne im Array)
- Tabelle: Download-Spalte 320px, 3-spaltiges Grid (5 Buttons → 3+2)
- Cards (Mobile) bleiben 2-spaltig (5 Buttons → 3 Zeilen)

lxc-frontend/app/services/pipeline.py

@@ -52,6 +52,7 @@ async def run_pipeline(job_id: int) -> None:
         existing_sum_path = _existing(job.summary_path)
         existing_pro_path = _existing(job.protocol_path)
         existing_dx_path  = _existing(job.docx_path)
+        existing_pdf_path = _existing(job.pdf_path)
 
     job_dir = settings.result_dir / str(job_id)
     job_dir.mkdir(parents=True, exist_ok=True)
@@ -103,14 +104,25 @@ async def run_pipeline(job_id: int) -> None:
         # 4) DOCX
         if existing_dx_path:
             log.info("[job %s] reuse docx %s", job_id, existing_dx_path.name)
-            _update(job_id, status=JobStatus.DONE, progress=100, error="")
         else:
             _update(job_id, status=JobStatus.EXPORTING, progress=90)
             log.info("[job %s] export docx", job_id)
             docx_bytes = await client.export_docx(protocol, profile=profile)
             docx_path = job_dir / "protocol.docx"
             docx_path.write_bytes(docx_bytes)
-            _update(job_id, docx_path=str(docx_path), status=JobStatus.DONE, progress=100, error="")
+            _update(job_id, docx_path=str(docx_path), progress=95)
+
+        # 5) PDF
+        if existing_pdf_path:
+            log.info("[job %s] reuse pdf %s", job_id, existing_pdf_path.name)
+            _update(job_id, status=JobStatus.DONE, progress=100, error="")
+        else:
+            _update(job_id, status=JobStatus.EXPORTING, progress=96)
+            log.info("[job %s] export pdf", job_id)
+            pdf_bytes = await client.export_pdf(protocol, profile=profile)
+            pdf_path = job_dir / "protocol.pdf"
+            pdf_path.write_bytes(pdf_bytes)
+            _update(job_id, pdf_path=str(pdf_path), status=JobStatus.DONE, progress=100, error="")
         log.info("[job %s] done", job_id)
     except Exception as e:  # noqa: BLE001
         log.exception("[job %s] failed", job_id)