Regenerate March 7 changelog with sandbox.env, CLI renames, and missing
accordion items. Add March 8 changelog for sandbox reliability and @file
validation. Update reference docs for --goal, --mode flags, sandbox.env,
checkpoint exclude globs, [log] config, [git.author], and project_memory.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>