Bump version to 0.6.0 and add CHANGELOG

Coordinated release of the free-threaded Python work:
  - PEP 703 audit + verification matrix (commits ae12bcf .. e619eaf)
  - Native AOT consumer sample (40fa61a)
  - Isolated-executor factory: Python.CreateIsolated() (74b572c)
  - Public-docs repositioning (b15f521)
  - HuggingFace semantic-search sample (f1d40f9)

CHANGELOG.md follows the Keep a Changelog format and records the
0.6.0 highlights — added APIs, fixed races, repositioned messaging,
new documentation, internal refactor, and the 3-way verification
matrix — plus stub entries for the most recent prior releases.

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

Release v0.5.2

Release v0.5.1

Disable symbols package for analyzer in project file