feat(plugins): add Cursor plugin manifest + refresh marketplace branding (#461)

Adds .cursor-plugin/plugin.json at the repo root alongside the existing
.codex-plugin/, so this repo is the single source of truth for the Codex
plugin AND the new Cursor Marketplace submission. Refreshes the shared
assets/logo.png + assets/icon.png to a 1024x1024 / 512x512 symbol-only
mark rasterized from docs/favicon.svg (white background), and renames the
marketplace display title from "HyperFrames" to "HyperFrames by HeyGen"
in both Codex and Cursor manifests.

No skill content changes; purely marketplace-visible branding and the new
Cursor manifest file.

.cursor-plugin/plugin.json

@@ -0,0 +1,31 @@
+{
+  "$schema": "https://cursor.com/schemas/cursor-plugin/plugin.json",
+  "name": "hyperframes",
+  "displayName": "HyperFrames by HeyGen",
+  "version": "0.1.0",
+  "description": "Write HTML, render video. Compositions, GSAP animations, captions, voiceovers, audio-reactive visuals, and website-to-video capture for HyperFrames.",
+  "author": {
+    "name": "HeyGen",
+    "email": "hyperframes@heygen.com"
+  },
+  "publisher": "HeyGen",
+  "homepage": "https://hyperframes.heygen.com",
+  "repository": "https://github.com/heygen-com/hyperframes",
+  "license": "Apache-2.0",
+  "logo": "assets/logo.png",
+  "category": "developer-tools",
+  "keywords": [
+    "hyperframes",
+    "video",
+    "html",
+    "gsap",
+    "animation",
+    "composition",
+    "rendering",
+    "captions",
+    "tts",
+    "audio-reactive"
+  ],
+  "tags": ["video", "animation", "design", "creative", "workflow"],
+  "skills": "./skills/"
+}