Adds early detection of version drift between README.md, marketplace.json,
and CHANGELOG.md at session start. When versions don't match, displays
a warning and suggests running /suggest-version to analyze and fix.
This addresses acceptance criteria #4 from issue #290:
- [x] SessionStart warns about version drift
Remaining criteria for future PRs:
- [ ] Version mismatch detected before commit (PreToolUse hook)
- [ ] /sprint-close includes version bump step (enforcement)
- [ ] Release workflow works with protected branches (PR creation)
Partial fix for #290
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>