Add binary exporters and template manager

- Native PDF exporter (cover, TOC, bookmarks, images, code, tables,
  text blocks); validated under Ghostscript
- Animated GIF exporter (title card, title overlay, progress bar)
- Image bundle exporter with watermark compositing
- DOCX and PPTX emitters (hand-built OOXML over our zip writer) with
  structural + relationship + XML well-formedness validation in tests
- Per-format template manager with .sfglt share archives
- Unified export dispatcher covering all nine formats
- 10 more workflow tests (52 total)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

exporters/gif.js

@@ -0,0 +1,87 @@
+'use strict';
+
+const fs = require('node:fs');
+const path = require('node:path');
+const { encodeGif } = require('../core/gif');
+const raster = require('../core/raster');
+const { guideSlug, renderAllImages } = require('./common');
+
+/**
+ * Animated GIF exporter: one frame per image step, optional title card,
+ * optional title overlay and progress bar per frame.
+ */
+
+const DEFAULT_TEMPLATE = {
+  width: 800,
+  frameDelayCs: 220,
+  loop: 0,
+  titleCard: true,
+  titleOverlay: true,
+  progressBar: true,
+  background: '#FFFFFF',
+};
+
+function exportGifGuide(ast, outDir, template = {}) {
+  const tpl = { ...DEFAULT_TEMPLATE, ...template };
+  const images = renderAllImages(ast);
+  const stepsWithImages = ast.steps.filter((s) => images.has(s.stepId));
+  if (!stepsWithImages.length) throw new Error('gif export: guide has no image steps');
+
+  // Frame height derives from the median aspect ratio so most shots fit.
+  const ratios = stepsWithImages.map((s) => {
+    const img = images.get(s.stepId);
+    return img.height / img.width;
+  }).sort((a, b) => a - b);
+  const ratio = ratios[Math.floor(ratios.length / 2)];
+  const W = tpl.width;
+  const H = Math.round(W * ratio) + (tpl.titleOverlay ? 36 : 0) + (tpl.progressBar ? 8 : 0);
+  const bg = raster.parseColor(tpl.background, [255, 255, 255, 255]);
+
+  const frames = [];
+
+  if (tpl.titleCard) {
+    const card = raster.createImage(W, H, [31, 41, 55, 255]);
+    raster.drawTextCentered(card, W / 2, H / 2 - 14, fitText(ast.guide.title, W, 22), 22, [255, 255, 255, 255]);
+    raster.drawTextCentered(card, W / 2, H / 2 + 18, `${stepsWithImages.length} steps`, 12, [156, 163, 175, 255]);
+    frames.push(card);
+  }
+
+  let n = 0;
+  for (const step of stepsWithImages) {
+    n += 1;
+    const frame = raster.createImage(W, H, bg);
+    const headerH = tpl.titleOverlay ? 36 : 0;
+    const footerH = tpl.progressBar ? 8 : 0;
+    const availH = H - headerH - footerH;
+
+    const src = images.get(step.stepId);
+    let dw = W, dh = Math.round((src.height / src.width) * W);
+    if (dh > availH) { dh = availH; dw = Math.round((src.width / src.height) * availH); }
+    const scaled = raster.resize(src, dw, dh);
+    raster.drawImage(frame, scaled, Math.round((W - dw) / 2), headerH + Math.round((availH - dh) / 2));
+
+    if (tpl.titleOverlay) {
+      raster.fillRect(frame, 0, 0, W, headerH, [31, 41, 55, 255]);
+      raster.drawText(frame, 10, 10, fitText(`${step.number}. ${step.title || ''}`, W - 20, 14), 14, [255, 255, 255, 255]);
+    }
+    if (tpl.progressBar) {
+      raster.fillRect(frame, 0, H - footerH, W, footerH, [229, 231, 235, 255]);
+      raster.fillRect(frame, 0, H - footerH, Math.round((W * n) / stepsWithImages.length), footerH, [37, 99, 235, 255]);
+    }
+    frames.push(frame);
+  }
+
+  fs.mkdirSync(outDir, { recursive: true });
+  const file = path.join(outDir, `${guideSlug(ast)}.gif`);
+  fs.writeFileSync(file, encodeGif(frames, { delayCs: tpl.frameDelayCs, loop: tpl.loop }));
+  return { file, frameCount: frames.length, width: W, height: H };
+}
+
+function fitText(text, maxWidthPx, sizePx) {
+  const scale = Math.max(1, Math.round(sizePx / 8));
+  const maxChars = Math.max(4, Math.floor(maxWidthPx / (8 * scale)) - 1);
+  const t = String(text);
+  return t.length > maxChars ? `${t.slice(0, maxChars - 1)}…` : t;
+}
+
+module.exports = { exportGifGuide, DEFAULT_TEMPLATE };