docs: publish strategy contract release line

[Pigbibi]

Summary

• document the finalized platform-strategy boundary in the shared package docs and readmes
• add explicit migration notes for adding a strategy profile, platform runtime, and upstream artifact provider
• bump QuantPlatformKit to v0.7.0 as the fixed-tag release line for the boundary refactor

Test Plan

• python3 - <<'PY'
  import tomllib
  data = tomllib.loads(open('pyproject.toml', 'rb').read().decode())
  assert data['project']['version'] == '0.7.0'
  PY
• git diff --check