docs: record post-v0.3 functional contract evidence

[CoderDeltaLAN]

Summary

Records post-v0.3.0 functional contract evidence for the current CLI command matrix.

Scope

• documents help, format, governance, dedupe, conflicts, explain, and init behavior verified locally
• records that init supports --dry-run and --write, not --force
• records sandbox-only init write and backup behavior
• updates CHANGELOG.md

Boundaries

• no runtime behavior change
• no release, tag, GitHub Release, or PyPI change
• no branch protection, CI policy, dependency, or security setting change

Verification

• full functional matrix passed locally
• 152 tests passed
• Ruff passed
• text hygiene passed
• git whitespace checks passed
• post-release audit passed