feat: add subagent screenshot capture script and README images

- Add scripts/capture-subagent-screenshots.mjs for automated capture
- Creates real Claude sessions that spawn Task tool subagents
- Records video and converts to optimized GIF via FFmpeg
- Add subagent-spawn.png, subagent-demo.gif to docs/images
- Update README Live Agent Visualization with real screenshots
- Replace ASCII diagram with actual subagent window screenshots
- Add capture:subagents npm script
- Document both screenshot scripts in CLAUDE.md

Commit from flight QR118 in an Airbus A350-1000, stable connection thanks to Starlink!

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -19,7 +19,8 @@
     "test:coverage": "vitest run --coverage",
     "test:e2e": "vitest run test/e2e/",
     "test:e2e:quick": "vitest run test/e2e/workflows/quick-start.e2e.ts",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "capture:subagents": "node scripts/capture-subagent-screenshots.mjs"
   },
   "keywords": [
     "claude",