feat(#180): PNG-Scorecards via WeasyPrint→PyMuPDF

PyMuPDF (fitz) ist bereits in requirements.txt — also kein extra
Dependency noetig. Render-Pipeline: HTML-Template → WeasyPrint-PDF →
fitz Pixmap → PNG-Bytes.

Endpoint: GET /api/assessment/scorecard.png?drucksache=&bundesland=
&format=og|square&scale=2.0
- scale=2.0 (Default) liefert Retina-Aufloesung.
- scale=1.0..4.0 erlaubt.

Refactor: gemeinsamer Helper _render_scorecard_pdf() fuer .pdf und .png
— vorher Code-Duplikat zwischen den Endpoints.

Refs: #179, #180

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/main.py

@@ -3413,30 +3413,25 @@ async def scorecard_template(
     })
 
 
-@app.get("/api/assessment/scorecard.pdf")
-async def api_scorecard_pdf(
-    drucksache: str, bundesland: str = "NRW", format: str = "og",
-):
-    """Liefert die Scorecard als PDF via WeasyPrint (#179).
+async def _render_scorecard_pdf(
+    drucksache: str, bundesland: str, format: str,
+) -> tuple[bytes, int, int, str]:
+    """Render Scorecard-HTML zu PDF (gemeinsamer Helper für .pdf und .png).
 
-    `format=og` → 1200×630pt, `format=square` → 1080×1080pt.
-
-    PNG-Render via Playwright wird in einem Folge-Issue ergänzt
-    (Container hat heute kein Chromium installiert).
+    Returns (pdf_bytes, width, height, safe_filename).
     """
-    from fastapi.responses import Response as _Response
     from weasyprint import HTML, CSS
+    from .models import Assessment
+
+    if format not in ("og", "square"):
+        raise HTTPException(status_code=400, detail="format muss 'og' oder 'square' sein")
+    width, height = ((1200, 630) if format == "og" else (1080, 1080))
+
     drucksache = validate_drucksache(drucksache)
     row = await get_assessment(drucksache)
     if not row:
         raise HTTPException(status_code=404, detail="Antrag nicht gefunden")
-    if format not in ("og", "square"):
-        raise HTTPException(status_code=400, detail="format muss 'og' oder 'square' sein")
 
-    width, height = ((1200, 630) if format == "og" else (1080, 1080))
-
-    # HTML aus dem internen Template ziehen (gleiche Logik wie /v2/scorecard).
-    from .models import Assessment
     assessment = Assessment.model_validate(row)
     matrix_lookup = {e.field: {"rating": e.rating} for e in assessment.gwoe_matrix}
     fraktionen = list(row.get("fraktionen", []) or [])
@@ -3461,20 +3456,63 @@ async def api_scorecard_pdf(
         fraktionen=fraktionen[:4],
         datum=(row.get("datum") or "")[:10],
         score_color=score_color,
-        width=width,
-        height=height,
+        width=width, height=height,
     )
 
-    # PDF mit exakt einer Seite in der Zielgrösse
     page_size_css = f"@page {{ size: {width}px {height}px; margin: 0; }}"
     pdf = HTML(string=html_content).write_pdf(stylesheets=[CSS(string=page_size_css)])
-    safe_name = drucksache.replace("/", "-")
+    safe = drucksache.replace("/", "-")
+    return pdf, width, height, f"scorecard-{safe}-{format}"
+
+
+@app.get("/api/assessment/scorecard.png")
+async def api_scorecard_png(
+    drucksache: str, bundesland: str = "NRW", format: str = "og", scale: float = 2.0,
+):
+    """Liefert die Scorecard als PNG via WeasyPrint→PyMuPDF.
+
+    `scale=2.0` rendert in doppelter Auflösung (für Retina-Displays).
+    """
+    from fastapi.responses import Response as _Response
+    pdf_bytes, width, height, safe_name = await _render_scorecard_pdf(
+        drucksache, bundesland, format,
+    )
+    try:
+        import fitz  # pymupdf
+        doc = fitz.open(stream=pdf_bytes, filetype="pdf")
+        page = doc[0]
+        # zoom-Matrix für höhere Auflösung
+        zoom = max(0.5, min(4.0, float(scale)))
+        mat = fitz.Matrix(zoom, zoom)
+        pix = page.get_pixmap(matrix=mat, alpha=False)
+        png = pix.tobytes("png")
+        doc.close()
+    except Exception as e:
+        logger.exception("PNG-Render fehlgeschlagen")
+        raise HTTPException(status_code=500, detail=f"PNG-Render-Fehler: {e}")
+    return _Response(
+        content=png, media_type="image/png",
+        headers={
+            "Content-Disposition": f'inline; filename="{safe_name}.png"',
+            "Cache-Control": "public, max-age=600",
+        },
+    )
+
+
+@app.get("/api/assessment/scorecard.pdf")
+async def api_scorecard_pdf(
+    drucksache: str, bundesland: str = "NRW", format: str = "og",
+):
+    """Liefert die Scorecard als PDF via WeasyPrint (#179).
+
+    `format=og` → 1200×630, `format=square` → 1080×1080.
+    """
+    from fastapi.responses import Response as _Response
+    pdf, _w, _h, safe_name = await _render_scorecard_pdf(drucksache, bundesland, format)
     return _Response(
         content=pdf, media_type="application/pdf",
         headers={
-            "Content-Disposition": (
-                f'inline; filename="scorecard-{safe_name}-{format}.pdf"'
-            ),
+            "Content-Disposition": f'inline; filename="{safe_name}.pdf"',
             "Cache-Control": "public, max-age=600",
         },
     )