Introduce semver release versioning (release commit for v1.0.0)

Version stamped in the FRAMEWORK.md header (the single source of the
framework version), CHANGELOG.md (Upstream-only), SDLC-release skill
(Upstream-only, removed at instantiation), and tag-pinned Quick Start.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>