Add Asciinema/GIF terminal demo to README

[singularityjason]

Description

Record a short (30-60 second) terminal demo showing Lightning Memory's MCP tools in action and add it to the README.

Acceptance Criteria

• Terminal recording using Asciinema, ttygif, or similar
• Shows: installing, starting the MCP server, storing a memory, querying it
• GIF or Asciinema embed added to README after the "Why?" section
• File added to assets/ directory

Tips

• Asciinema for recording
• agg to convert to GIF
• Keep it under 60 seconds — show the value fast