docs(plan): canonical examples/chat demo (Phase 1) implementation plan

Bite-sized tasks across 7 phases (scaffolding → python → angular bones
→ wire-up → smoke CLI → cleanup → README + validation) with full code
samples inline, TDD where applicable, exact commands and expected
output. Replaces stale examples/chat-agent. No version pins (smoke
template uses `*` placeholder, demo uses workspace `*`).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: blove