feat(remotion): +ProductShowcase block (phone/browser device mockup)

Adds the product/app-showcase template type the engine was missing: a 2.5D device
frame (rounded phone with notch, or a browser window with traffic-lights + URL bar)
holding an uploaded screenshot, with title/subtitle and the shared Three backdrop.
Fields: screenshot, title, subtitle, device (phone|browser). Registry now 9 blocks.
Verified via FlexStory props-override stills (both device modes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/remotion/src/scenes/registry.ts

@@ -7,6 +7,7 @@ import { SlideshowBlock } from "./blocks/Slideshow";
 import { OutroCTABlock } from "./blocks/OutroCTA";
 import { LogoRevealBlock } from "./blocks/LogoReveal";
 import { StatCounterBlock } from "./blocks/StatCounter";
+import { ProductShowcaseBlock } from "./blocks/ProductShowcase";
 
 /**
  * The scene-block registry. A FlexStory template is an ordered list of these
@@ -22,6 +23,7 @@ export const SCENE_BLOCKS: Record<string, SceneBlock> = {
   [OutroCTABlock.id]: OutroCTABlock,
   [LogoRevealBlock.id]: LogoRevealBlock,
   [StatCounterBlock.id]: StatCounterBlock,
+  [ProductShowcaseBlock.id]: ProductShowcaseBlock,
 };
 
 export const BLOCK_LIST = Object.values(SCENE_BLOCKS);