feat(cli): add shared PDF-to-image rendering and document usage

add shared render_pdf_pages helper for consistent rasterization
reuse the same renderer in regression test and CLI flow
add new render-image CLI command to export PDF pages as PNG
support single-page render (--page) and full export (--all-pages)
add configurable output path and DPI options
document the new rendering command and options in README

schema.json

@@ -85,6 +85,11 @@
             "type": "boolean",
             "description": "true = Dropdown-Anzeigewerte ins PDF schreiben (z.B. 'X = anwesend'); false = rohe Export-Werte (z.B. 'X')",
             "default": true
+        },
+        "pdf_need_appearances": {
+            "type": "boolean",
+            "description": "Steuert AcroForm /NeedAppearances beim Schreiben der PDF. false wird fuer stabile PyMuPDF-Render bevorzugt (Footer/Buttons sichtbar).",
+            "default": false
         }
     }
 }