release: agent-first-data v0.8.0

- Add cli_render_help and cli_render_help_markdown as optional Rust APIs (cli-help and cli-help-markdown features) for recursive help rendering — agents read --help once and get all subcommands and flags expanded in a single output, with scoping support for subcommand-level help
- Harden secret redaction across the Rust, Go, Python, and TypeScript libraries so _secret-suffixed fields cannot leak: render JSON/YAML/plain output from sanitized redacted copies so key-name collisions cannot restore raw secret values, make Go YAML/plain fallbacks type-only so Stringer and unsupported struct values cannot stringify raw fields, escape logfmt plain values to preserve one record per line, and add a strict redaction mode with shared cross-language test fixtures