Add guide metadata, redesign PDF cover, paginate steps per-page, and run exports in a helper process

Lets users record author/co-authors/organization for a guide via a new
"Guide information…" dialog; this metadata renders below the title on
the PDF cover (title now sits above the accent rule). PDF export also
paginates so each step fits its own page where possible, keeps a
step's title/image/lead-in together, and forces the next step onto a
fresh page after an oversized step overflows. Exports now run in a
forked helper process so large guides no longer freeze the UI.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

app/main.js

@@ -14,6 +14,7 @@ const { SearchIndex } = require('../core/search');
 const { TemplateManager, FORMATS } = require('../core/templates');
 const { buildRenderAst } = require('../core/renderast');
 const { runExport, EXPORTERS } = require('../exporters');
+const { runExportInWorker } = require('./export-runner');
 const { exportGuideArchive, importGuideArchive, saveLinkedGuide, readArchive } = require('../core/archive');
 const { createSnapshot, listSnapshots, restoreSnapshot } = require('../core/snapshots');
 const { readLock } = require('../core/locks');
@@ -607,8 +608,14 @@ function setupIpc() {
       dir = res.filePaths[0];
     }
     settings.set(`exports.lastOutputDirs.${format}`, dir);
-    const ast = buildRenderAst(store, guideId, { globals: settings.getGlobalPlaceholders() });
-    const result = runExport(format, ast, dir, options || {});
+    const result = await runExportInWorker({
+      dataDir: store.root,
+      guideId,
+      format,
+      options: options || {},
+      outDir: dir,
+      globals: settings.getGlobalPlaceholders(),
+    });
     if (settings.get('exports.openFolderAfterExport')) shell.showItemInFolder(result.file);
     return { ok: true, ...result };
   });