Create VHS terminal demo GIF for README

[EtanHey]

The README would benefit from a 15-30 second terminal demo GIF showing BrainLayer in action.

Tool: VHS — records terminal sessions as GIFs from a tape file.

Suggested flow:

1. `brainlayer search "how did I implement auth"` — show search results
2. `brainlayer stats` — show the 268K+ chunks, enrichment stats
3. Brief MCP tool usage example

Scope:

• Create `demo.tape` VHS script
• Generate GIF and add to `docs/assets/`
• Embed in README under the Quick Start section

Getting started:

• Install VHS: `brew install charmbracelet/tap/vhs`
• See `brainlayer --help` for available commands
• The search and stats commands produce the most visual output