feat: add Ken Burns effect, fix caption visibility and Facebook binary upload

- Add slow zoom/pan (Ken Burns) effect to each image slide, cycling through
  8 deterministic presets per image index for natural variety
- CapCut-style captions: semi-transparent pill background + yellow glow on
  active word; background/text now only visible while voice is speaking
- Fix Facebook error 6000: pass Node.js Buffer directly instead of unsafe
  ArrayBuffer pool-slice conversion which could corrupt the upload payload
- Fix TypeScript error: replace u-flag emoji regex with BMP surrogate pairs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/remotion/ImageComposition.tsx

@@ -165,27 +165,13 @@ export const ImageComposition = ({
     ? wordTimings.findIndex(w => frame >= w.startFrame && frame < w.endFrame)
     : -1;
 
-  // Determine which group is currently active
-  const currentGroupIdx = activeWordIdx >= 0 ? Math.floor(activeWordIdx / WORDS_PER_GROUP) : -1;
+  // Only show caption when a word is actively being spoken
+  const renderCaption = frame < endingStart && activeWordIdx >= 0;
 
-  // Determine the last group that was visible (for holding display between words)
-  const lastActiveWordIdx = wordTimings
-    ? [...wordTimings].reverse().findIndex(w => frame >= w.startFrame)
-    : -1;
-  const resolvedLastIdx = lastActiveWordIdx >= 0 && wordTimings
-    ? wordTimings.length - 1 - lastActiveWordIdx
-    : -1;
-  const displayGroupIdx = activeWordIdx >= 0
-    ? currentGroupIdx
-    : resolvedLastIdx >= 0
-      ? Math.floor(resolvedLastIdx / WORDS_PER_GROUP)
-      : -1;
-
-  const renderCaption = frame < endingStart && wordTimings && wordTimings.length > 0 && displayGroupIdx >= 0;
-
-  const groupStart = displayGroupIdx * WORDS_PER_GROUP;
+  const groupIdx = activeWordIdx >= 0 ? Math.floor(activeWordIdx / WORDS_PER_GROUP) : 0;
+  const groupStart = groupIdx * WORDS_PER_GROUP;
   const groupWords = wordTimings ? wordTimings.slice(groupStart, groupStart + WORDS_PER_GROUP) : [];
-  const activeIdxInGroup = activeWordIdx >= 0 ? activeWordIdx - groupStart : -1;
+  const activeIdxInGroup = activeWordIdx - groupStart;
 
   // First frame of the current group (for fade-in)
   const groupFirstFrame = groupWords.length > 0 ? groupWords[0].startFrame : 0;

server/routes/remotion.ts

@@ -378,8 +378,7 @@ remotionRouter.post("/publish", async (req, res) => {
           console.log(`🚀 Publishing to ${page.pageName} (direct binary upload)...`);
           // Upload video bytes directly — Facebook cannot access local URLs
           const videoBuffer = await fs.promises.readFile(localPath);
-          const arrayBuffer = videoBuffer.buffer.slice(videoBuffer.byteOffset, videoBuffer.byteOffset + videoBuffer.byteLength) as ArrayBuffer;
-          const reelId = await facebookService.publishVideoFromBuffer(page, arrayBuffer, description || "");
+          const reelId = await facebookService.publishVideoFromBuffer(page, videoBuffer, description || "");
           await dbStorage.updateScheduledPost(scheduledPost.id, { publishedAt: new Date(), externalPostId: reelId });
           results.push({ pageId, success: true, reelId });
         } else {

server/services/facebook.ts

@@ -78,8 +78,7 @@ export class FacebookService {
         ? path.join(process.cwd(), videoMedia.originalUrl)
         : videoMedia.originalUrl;
       const nodeBuffer = await fs.promises.readFile(localPath);
-      const arrayBuffer = nodeBuffer.buffer.slice(nodeBuffer.byteOffset, nodeBuffer.byteOffset + nodeBuffer.byteLength) as ArrayBuffer;
-      return await this.publishVideoFromBuffer(page, arrayBuffer, post.content);
+      return await this.publishVideoFromBuffer(page, nodeBuffer, post.content);
     } else {
       // Default to feed
       const imageMedia = mediaList.filter(m => m.type === 'image');
@@ -568,7 +567,7 @@ export class FacebookService {
    */
   async publishVideoFromBuffer(
     page: SocialPage,
-    videoBuffer: ArrayBuffer,
+    videoBuffer: Buffer | ArrayBuffer,
     description?: string
   ): Promise<string> {
     if (!page.accessToken) throw new Error('No access token found for this page');