M4.31: Save PDF dialog and document.exportPdf with PDF settings

PdfSettings (serde, camelCase) is the Save PDF model: Standard, Compatibility
PDF 1.4-2.0, General (Preserve editing, Thumbnails, Fast web view, View after
saving, Create layers), Compression, Marks and Bleeds, Output, Advanced and
Security. PdfOptions = settings + pages, title and date.

document.exportPdf {path?, preset?, artboard?|artboards?|range?, standard?,
compatibility?, ...sections} -> {path|dataBase64, bytes, warnings} applies the
options over the preset (null keeps the preset's value); PDF/X, passwords,
PDF/A-2b at 2.0 and out-of-range values are refused; options accepted but not
applied yet come back as warnings. document.export {format: pdf} and
document.formats take and list the same options.

The Save PDF dialog (file.export.pdf, ui.savePdfDialog) has Preset,
Standard and Compatibility on top and a section list; it runs the export
before asking for a path, so bad options never open a save dialog.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/fileio/encode.rs

@@ -8,7 +8,6 @@ use vectorcraft_doc::Document;
 
 use super::super::*;
 use super::Format;
-use crate::EngineError;
 
 const C: &str = "document.export";
 
@@ -113,11 +112,7 @@ pub fn encode(doc: &Document, format: &str, p: &Value) -> Result<Vec<u8>> {
             let opts = vectorcraft_svg::ExportOptions { artboard, outline_text: o.outline_text.unwrap_or(false), ..Default::default() };
             vectorcraft_svg::export(doc, &opts).into_bytes()
         }
-        "pdf" => {
-            let o: ArtboardPick = options(f, p)?;
-            let opts = vectorcraft_pdf::PdfOptions { artboards: boards(o.resolve(n))?, ..Default::default() };
-            super::super::rasterfx::export_pdf(doc, &opts).map_err(|e| EngineError::Other(e.to_string()))?
-        }
+        "pdf" => super::pdf::encode(C, doc, p)?.0,
         "png" | "jpg" | "webp" => {
             let o: RasterOptions = options(f, p)?;
             let region = doc.artboards[boards(o.boards.one(n))?].rect;