README rewrite: ecosystem hub with TS-first quick start

- Repositioned as ecosystem hub (spec + TS SDK + web editor)
- Leads with TypeScript Quick Start (not Python redirect)
- One-line MCP redirect for Python developers (blockquote)
- Ecosystem table: all 3 packages + flowscript.org
- Notation section with "optional" anxiety defuser
- Web editor showcase with screenshot
- 142 lines (was 800+), 3-agent consultation reviewed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: phillipclapham