v0.7.0

feat: v0.7.0 — chat session hardening, validated atoms, navigation fixes

- Refactored useChatSession into smaller focused hooks
- Added validated-atom pattern for runtime type safety on persistent atoms
- Fixed navigation edge cases (commit envelope, ephemeral resets)
- Hardened flow routing with proper transaction guards
- Removed deprecated useWorkflowReset in favor of inline reset logic
- Added comprehensive test coverage: 13 new test files with fixtures
- Shared test utilities (test-utils.tsx, vitest-setup.ts)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>